Halacha

הלכה א
הָאוֹכֵל כְּזַיִת מִבְּשַׂר בְּהֵמָה שֶׁמֵּתָה אוֹ חַיָּה שֶׁמֵּתָה אוֹ עוֹף שֶׁמֵּת לוֹקֶה שֶׁנֶּאֱמַר (דברים יד כא) "לֹא תֹאכְלוּ כָל נְבֵלָה". וְכָל שֶׁלֹּא נִשְׁחֲטָה כָּרָאוּי הֲרֵי זוֹ מֵתָה. וּבְהִלְכוֹת הַשְּׁחִיטָה יִתְבָּאֵר הַשְּׁחִיטָה שֶׁהִיא כָּרָאוּי וְשֶׁאֵינָהּ כָּרָאוּי:
כסף משנה
1.
A person who partakes of an olive-sized portion of a domesticated animal, wild beast, or fowl which dies is liable for lashes, as [Deuteronomy 14:21] states: "Do not partake of any nevelah."1Sefer HaMitzvot (negative commandment 180) and Sefer HaChinuch (mitzvah 472) include this among the 613 mitzvot of the Torah. All animals that were not slaughtered in the appropriate manner are considered as if they died. In the Laws of Shechitah, we will explain which types of slaughter are appropriate and which are not.

הלכה ב
אֵין אָסוּר מִשּׁוּם נְבֵלָה אֶלָּא מִינִים טְהוֹרִים בִּלְבַד מִפְּנֵי שֶׁהֵן רְאוּיִין לִשְׁחִיטָה וְאִם נִשְׁחֲטוּ שְׁחִיטָה כְּשֵׁרָה יִהְיוּ מֻתָּרִין בַּאֲכִילָה. אֲבָל מִינִין טְמֵאִין שֶׁאֵין שְׁחִיטָה מוֹעֶלֶת בָּהֶן בֵּין שֶׁנִּשְׁחֲטָה כָּרָאוּי בֵּין שֶׁמֵּתָה כְּדַרְכָּהּ בֵּין שֶׁחָתַךְ בָּשָׂר מִן הַחַי מִמֶּנָּה וַאֲכָלוֹ אֵינוֹ לוֹקֶה מִשּׁוּם נְבֵלָה וּטְרֵפָה אֶלָּא מִשּׁוּם אוֹכֵל בְּשַׂר טְמֵאָה:
כסף משנה
2.
Only animals from kosher species are forbidden as a nevelah, for they are the species that are fit to be ritually slaughtered and if they are slaughtered in a kosher manner, it is permitted to partake of them. [When,] by contrast, one partakes of [meat from] a non-kosher species, [since] ritual slaughter is of no consequence with regard to them, whether they are slaughtered in a kosher manner, whether they died in a natural manner, or whether one cut meat from a living animal and ate it, one does not receive lashes for partaking of a nevelah or partaking of trefe meat,2See Halachah 10. only because one ate the meat of a non-kosher animal.3From Chullin 100b, it would appear that the rationale for this ruling is the general principle: "One prohibition does not fall upon another prohibition." Since the meat is already prohibited because it is from a non-kosher species, the prohibition of nevela does not apply to it. The Rambam's wording, however, is slightly different and may be alluding to a slightly different rationale.

הלכה ג
הָאוֹכֵל עוֹף טָהוֹר חַי כָּל שֶׁהוּא לוֹקֶה מִשּׁוּם אוֹכֵל נְבֵלָה וְאַף עַל פִּי שֶׁאֵין בּוֹ כְּזַיִת הוֹאִיל וַאֲכָלוֹ כֻּלּוֹ. וְאִם אֲכָלוֹ אַחַר שֶׁמֵּת עַד שֶׁיִּהְיֶה בּוֹ כְּזַיִת. וְאַף עַל פִּי שֶׁאֵין בְּכֻלּוֹ בָּשָׂר כְּזַיִת הוֹאִיל וְיֵשׁ בְּכֻלּוֹ כְּזַיִת חַיָּב עָלָיו מִשּׁוּם נְבֵלָה:
כסף משנה
3.
When a person eats an [entire] kosher fowl4Which was not correctly slaughtered. of any size, he is liable for lashes for partaking of a nevelah, even though he ate less than an olive-sized portion. [The rationale is that] he consumed it in its entirety.5This reflects a general concept with regard to the laws of kashrut. As stated in Chapter 2, Law 21, whenever "one eats an entire forbidden creature by itself, one is liable for lashes according to Scriptural Law even if it is smaller than a mustard seed."
The commentaries (Maggid Mishneh, Rav Moshe HaCohen) question why the Rambam states that the person is liable for eating a nevelah. Seemingly, the prohibition he transgresses is eating a limb from a living animal (see Chapter 5). The Meiri explains the Rambam's position, stating that an entire creature cannot be considered as "a limb."
If he ate it after it died, it must be the size of an olive [for him to be liable].6For the conception of being liable for an entire creature even though it is not the size of an olive, applies only when that creature is inherently forbidden (Meiri). While alive, the bird is considered as an entire forbidden entity, like a non-kosher species. After its death, that distinction does not apply. Even though it does not have an olive-sized portion of meat on it, since as a whole, it is the size of an olive, he is liable for [partaking of] a nevelah.7For we include the bones and the sinews as well (Chullin 102b).

הלכה ד
הָאוֹכֵל כְּזַיִת מִבְּשַׂר נֵפֶל בְּהֵמָה טְהוֹרָה לוֹקֶה מִשּׁוּם אוֹכֵל נְבֵלָה. וְאָסוּר לֶאֱכל מִן הַבְּהֵמָה שֶׁנּוֹלְדָה עַד לֵיל שְׁמִינִי שֶׁכָּל שֶׁלֹּא שָׁהָה שְׁמוֹנָה יָמִים בִּבְהֵמָה הֲרֵי זֶה כְּנֵפֶל. וְאֵין לוֹקִין עָלָיו. וְאִם נוֹדַע לוֹ שֶׁכָּלוּ לוֹ חֳדָשָׁיו בַּבֶּטֶן וְאַחַר כָּךְ נוֹלַד שֶׁהֵן תִּשְׁעָה חֳדָשִׁים לִבְהֵמָה גַּסָּה וַחֲמִשָּׁה לְדַקָּה הֲרֵי זֶה מֻתָּר בַּיּוֹם שֶׁנּוֹלַד:
כסף משנה
4.
When a person partakes of an olive-sized portion of a stillborn fetus8The same laws apply if the fetus is born alive, but it is obvious that the birth is not viable. Even if the animal is slaughtered in the appropriate manner, we are forbidden to partake of it. of a kosher animal, he is liable for lashes for partaking of a nevelah.
It is forbidden to partake of a newborn animal until the night of the eighth day [of its life].9I.e., even if the animal is slaughtered properly, it is forbidden because it is possible that the birth is not viable. Although our Sages (Chulin 136a) spoke of the eighth day of an animal's life, their intent was the beginning of the eighth day (Maggid Mishneh). For whenever an animal has not lived for eight days, we consider it as stillborn, but lashes are not administered [for partaking] of it.10Since it is not a definite matter, lashes are not administered (ibid.). [Moreover,] if it is known that the animal was born after a full term period of gestation, i.e., nine months for a large domesticated animal and five months for a small domesticated animal, it is permitted on the day that it was born.11In contrast, an animal may not be offered as a sacrifice until the eighth day of its life (Exodus 22:29; Turei Zahav 15:3).

הלכה ה
הַשִּׁלְיָא שֶׁיָּצָאת עִם הַוָּלָד אֲסוּרָה בַּאֲכִילָה וְהָאוֹכְלָהּ פָּטוּר שֶׁאֵינָהּ בָּשָׂר:
כסף משנה
5.
The placenta that is expelled together with the newborn is forbidden to be eaten. A person who eats it, however, is not liable,12I.e., he is not considered to have partaken of a nevelah. because it is not [considered] meat.13For as stated in Halachah 18, these are not considered meat, but rather comparable to an animal's wastes. For that reason, the Ra'avad (in his gloss to Chapter 5, Halachah 13) states that there is no prohibition against partaking of a placenta.

הלכה ו
הָאוֹכֵל כְּזַיִת מִבְּשַׂר בְּהֵמָה אוֹ חַיָּה אוֹ עוֹף טְהוֹרִים שֶׁנִּטְרְפוּ לוֹקֶה שֶׁנֶּאֱמַר (שמות כב ל) "וּבָשָׂר בַּשָּׂדֶה טְרֵפָה לֹא תֹאכֵלוּ לַכֶּלֶב תַּשְׁלִכוּן אֹתוֹ". טְרֵפָה הָאֲמוּרָה בַּתּוֹרָה זוֹ שֶׁטָּרְפָה אוֹתָהּ חַיַּת הַיַּעַר כְּגוֹן אֲרִי וְנָמֵר וְכַיּוֹצֵא בָּהֶן. וְכֵן עוֹף שֶׁטָּרַף אוֹתוֹ עוֹף הַדּוֹרֵס כְּגוֹן נֵץ וְכַיּוֹצֵא בּוֹ. וְאֵין אַתָּה יָכוֹל לוֹמַר שֶׁטָּרְפָה אוֹתָהּ וְהֵמִיתָה אוֹתָהּ שֶׁאִם מֵתָה הֲרֵי הִיא נְבֵלָה. וּמַה לִּי מֵתָה מֵחֲמַת עַצְמָהּ אוֹ הִכָּה בְּסַיִף וֶהֱמִיתָהּ אוֹ שְׁבָרָהּ אֲרִי וֶהֱמִיתָהּ. הָא אֵינוֹ מְדַבֵּר אֶלָּא בְּשֶׁנִּטְרְפָה וְלֹא מֵתָה:
כסף משנה
6.
When a person eats an olive-sized portion of a kosher14I.e., like the prohibition of nevelah, the prohibition of trefe does not apply with regard to non-kosher species. domesticated animal, wild beast, or fowl that was mortally wounded is liable for lashes, as [Exodus 22:30] states: "Do not eat meat [from an animal that was] mortally wounded (trefe) in the field. Cast it to the dogs."15I.e., even if it was slaughtered properly before it died, the meat is, nevertheless, forbidden, as stated in the following halachah. Sefer HaMitzvot (negative commandment 181) and Sefer HaChinuch (mitzvah 73) include this among the 613 mitzvot of the Torah.
The term trefe employed by the Torah refers to [an animal] mortally wounded by a wild beast, e.g., a lion, a tiger, or the like, or a fowl mortally wounded by a bird of prey, e.g., a hawk or the like.16As the Rambam proceeds to explain in Halachah 8, the term trefe also applies in other situations. Nevertheless, there is an added dimension of severity to the laws applying to animals that are mortally wounded by beasts, as stated in Hilchot Shechitah 5:3 (Maggid Mishneh; Kessef Mishneh). We cannot say that the term trefe refers to an animal that was attacked and killed, for if it died, it is a nevelah. What difference does it make if it died naturally, was struck by a sword or died, or was battered by a lion and died? Thus [the term trefe] must refer to an instance when it was mortally wounded, but did not die.

הלכה ז
וְאִם הַטְּרֵפָה שֶׁלֹּא מֵתָה אֲסוּרָה יָכוֹל אִם בָּא זְאֵב וְגָרַר הַגְּדִי בְּרַגְלוֹ אוֹ בִּזְנָבוֹ אוֹ בְּאָזְנוֹ וְרָדַף אָדָם וְהִצִּילוֹ מִפִּיו יִהְיֶה אָסוּר שֶׁהֲרֵי נִטְרַף תַּלְמוּד לוֹמַר (שמות כב ל) "וּבָשָׂר בַּשָּׂדֶה טְרֵפָה" וְגוֹ' (שמות כב ל) "לַכֶּלֶב תַּשְׁלִיכוּן אֹתוֹ". עַד שֶׁיַּעֲשֶׂה אוֹתָהּ בָּשָׂר הָרְאוּיָה לַכֶּלֶב. הָא לָמַדְתָּ שֶׁהַטְּרֵפָה הָאֲמוּרָה בַּתּוֹרָה הִיא שֶׁטָּרְפָה אוֹתוֹ חַיַּת הַיַּעַר וְשָׁבְרָה אוֹתָהּ וְנָטָה לָמוּת וַעֲדַיִן לֹא מֵתָה. אַף עַל פִּי שֶׁקָּדַם וּשְׁחָטָהּ קֹדֶם שֶׁתָּמוּת הֲרֵי זוֹ אֲסוּרָה מִשּׁוּם טְרֵפָה הוֹאִיל וְאִי אֶפְשָׁר שֶׁתִּחְיֶה מִמַּכָּה זוֹ הַבָּאָה עָלֶיהָ:
כסף משנה
7.
If an animal that is mortally wounded is forbidden, shall we say that if a wolf or a lion comes and drags a kid by its foot, its tail, or its ear, and a man pursues [the beast] and saves [the kid], it will be forbidden, because it was attacked?17The term trefe literally means "preyed upon." Our translation "mortally wounded" is the halachic definition as the Rambam proceeds to explain. The Torah states: "Do not eat meat [from an animal that was] mortally wounded (trefe) in the field. Cast it to the dogs." [An animal is not considered trefe] unless it was brought to a state that its meat is fit [only] for the dogs. Thus we have learned that the term trefe employed by the Torah refers to [an animal] that was attacked by a wild beast and battered by it that has not died yet. Even if the person hurries and slaughters it before it dies, it is forbidden as trefe. For it is impossible that it will live after suffering such wounds.

הלכה ח
נִמְצֵאתָ לָמֵד שֶׁהַתּוֹרָה אָסְרָה הַמֵּתָה וְהִיא הַנְּבֵלָה. וְאָסְרָה הַנּוֹטָה לָמוּת מֵחֲמַת מַכּוֹתֶיהָ וְאַף עַל פִּי שֶׁעֲדַיִן לֹא מֵתָה וְהִיא הַטְּרֵפָה. וּכְשֵׁם שֶׁלֹּא תַּחֲלֹק בְּמִיתָה בֵּין מֵתָה מֵחֲמַת עַצְמָהּ בֵּין שֶׁנָּפְלָה וָמֵתָה בֵּין שֶׁחֲנָקָהּ עַד שֶׁמֵּתָה בֵּין שֶׁדְּרָסַתָּה חַיָּה וַהֲרָגַתָּה. כָּךְ לֹא תַּחֲלֹק בְּנוֹטָה לָמוּת בֵּין שֶׁטְּרָפַתָּה חַיָּה וּשְׁבָרַתָּה בֵּין שֶׁנָּפְלָה מִן הַגַּג וְנִשְׁתַּבְּרוּ רֹב צַלְעוֹתֶיהָ בֵּין שֶׁנָּפְלָה וְנִתְרַסְּקוּ אֵיבָרֶיהָ בֵּין שֶׁזָּרַק בָּהּ חֵץ וְנָקַב לִבָּהּ אוֹ רֵאָתָהּ בֵּין שֶׁבָּא לָהּ חלִי מֵחֲמַת עַצְמָהּ וְנָקַב לִבָּהּ אוֹ רֵאָתָהּ אוֹ שִׁבֵּר רֹב צַלְעוֹתֶיהָ וְכַיּוֹצֵא בָּהֶן. הוֹאִיל וְהִיא נוֹטָה לָמוּת מִכָּל מָקוֹם הֲרֵי זוֹ טְרֵפָה. בֵּין שֶׁהָיָה הַגּוֹרֵם בִּידֵי בָּשָׂר וָדָם בֵּין שֶׁהָיָה בִּידֵי שָׁמַיִם. אִם כֵּן לָמָּה נֶאֱמַר בַּתּוֹרָה (שמות כב ל) "טְרֵפָה". דִּבֵּר הַכָּתוּב בַּהוֹוֶה. שֶׁאִם לֹא תֹּאמַר כֵּן לֹא תֵּאָסֵר אֶלָּא אוֹתָהּ שֶׁנִּטְרְפָה בַּשָּׂדֶה אֲבָל אִם נִטְרְפָה בֶּחָצֵר לֹא תֵּאָסֵר. הָא לָמַדְתָּ שֶׁאֵין הַכָּתוּב מְדַבֵּר אֶלָּא בַּהוֹוֶה:
כסף משנה
8.
Thus we have learned that the Torah forbade [an animal] that died, a nevelah, and it forbade one that was on the verge of death because of its wounds even though it has not died yet, i.e., a trefe.
Now we do not make a distinction with regard to an animal that has died regardless of whether it died naturally, it fell and died, it was strangled until it died, or it was attacked by a wild beast who killed it. Similarly, we do not make a distinction between an animal that is on the verge of death, regardless of whether it was attacked by an animal and battered, fell from the roof and broke the majority of its ribs,18This and the following examples are specifically mentioned by the Rambam in Hilchot Shechitah 10:1, 9:8, 11:4, 6:1. fell and crushed its limbs, it was shot with an arrow and its heart or lung pierced, it developed an illness that caused its heart or lung to be perforated, one broke the majority of its ribs, or the like. Since it is on the verge of death regardless of the cause, it is a trefe. [This applies] whether [its wound] was caused by flesh and blood or by God's hand.
If so, why does the Torah use the term trefe? For Scripture speaks with regard to prevalent situations.19This is a general principle employed by our Sages with regard to the interpretation of the Torah's language. When it mentions a specific situation, it is not confining itself to the limited setting mentioned in the verse, but applies to other circumstances as well. Why is that situation mentioned? Because it is common. [We are forced] to say this. If not, only an animal that was mortally wounded in the field would be forbidden.20For only that is in the direct scope of the verse. One that is mortally wounded in a courtyard would not be forbidden. Thus we learn that Scripture [is employing this example,] only because it speaks with regard to prevalent situations.

הלכה ט
וְעִנְיַן הַכָּתוּב שֶׁהַנּוֹטָה לָמוּת מֵחֲמַת מַכּוֹתֶיהָ וְאִי אֶפְשָׁר לָהּ לִחְיוֹת מֵחֲמַת מַכָּה זוֹ אֲסוּרָה. מִכָּאן אָמְרוּ חֲכָמִים זֶה הַכְּלָל כָּל שֶׁאֵין כָּמוֹהָ חַיָּה טְרֵפָה. וּבְהִלְכוֹת שְׁחִיטָה יִתְבָּאֵר אֵי זֶה חלִי עוֹשֶׂה אוֹתָהּ טְרֵפָה וְאֵי זֶה חלִי אֵין עוֹשֶׂה אוֹתָהּ טְרֵפָה:
כסף משנה
9.
The intent of the verse is that [an animal] that is mortally wounded and will not live21Longer than twelve months (Hilchot Shechitah 11:1). because of these wounds is forbidden. On this basis, our Sages said:22Chulin 42a. "This is the general principle: Whenever [an animal] in this condition will not live, it is trefe." In Hilchot Shechitah,23From Chapter Five to Chapter Eleven. A concise list is found in Chapter 10, Halachah 9. we will explain which conditions cause an animal to be deemed trefe and which do not cause it to be deemed trefe.

הלכה י
וְכֵן הַחוֹתֵךְ בָּשָׂר מִן הַחַי מִן הַטְּהוֹרִים הֲרֵי אוֹתוֹ הַבָּשָׂר טְרֵפָה וְהָאוֹכֵל מִמֶּנּוּ כְּזַיִת לוֹקֶה מִשּׁוּם אוֹכֵל טְרֵפָה. שֶׁהֲרֵי בָּשָׂר זֶה מִבְּהֵמָה שֶׁלֹּא נִשְׁחֲטָה וְלֹא מֵתָה. מַה לִּי טָרְפָה אוֹתָהּ חַיָּה מַה לִּי חֲתָכָהּ בְּסַכִּין מַה לִּי בְּכֻלָּהּ מַה לִּי בְּמִקְצָתָהּ. הֲרֵי הוּא אוֹמֵר (שמות כב ל) "וּבָשָׂר בַּשָּׂדֶה טְרֵפָה לֹא תֹאכֵלוּ" כֵּיוָן שֶׁנַּעֲשֵׂית הַבְּהֵמָה בָּשָׂר בַּשָּׂדֶה הֲרֵי הִיא טְרֵפָה:
כסף משנה
10.
Similarly, when one cuts meat from a living kosher24For as mentioned above, the prohibition against partaking of a trefe applies only with regard to kosher animals. animal, one receives lashes for partaking of a trefe.25See Chapter Five, Halachot 2-3, where the Rambam distinguishes between this prohibition and the prohibition against partaking of a limb from a living animal. Note, however, Hilchot Melachim 9:10-11 where the Rambam includes eating the meat from an animal and eating a limb from an animal as a single prohibition for a gentile. For this meat comes from an animal that has not been ritually slaughtered and has not died. [Hence it is comparable to a trefe.] What difference does it make to me if it was attacked by an animal or cut by a knife? And what difference does it make if [the animal] was [wounded] in its totality or only a portion of it was wounded?26I.e., just as we forbid the meat of an animal that was mortally wounded, we should forbid a portion of meat that was cut off with a knife. For the verse states: "Do not eat meat [from an animal that was] trefe in the field." Since [a portion of] the animal was made meat in the field,27I.e., the meat was cut off from its natural place. See also Chapter 5, Halachah 9. it is trefe.

הלכה יא
בְּהֵמָה שֶׁהִיא חוֹלָה מֵחֲמַת שֶׁתָּשַׁשׁ כֹּחָהּ וְנָטְתָה לָמוּת הוֹאִיל וְלֹא אֵרְעָה מַכָּה בְּאֵיבָר מֵאֵיבָרֶיהָ הַמְּמִיתִים אוֹתָהּ הֲרֵי זוֹ מֻתֶּרֶת. שֶׁלֹּא אָסְרָה תּוֹרָה אֶלָּא כְּעֵין טְרֵפַת חַיַּת הַיַּעַר שֶׁהֲרֵי עָשָׂה בָּהּ מַכָּה הַמְּמִיתָה אוֹתָהּ:
כסף משנה
11.
When an animal is sick because it is weakened and is on the verge of death, it is permitted, because it did not suffer a wound in any one of the limbs and organs that will cause it to die. For the Torah forbade only those situations resembling an animal mortally wounded by a preying wild beast. In that situation, the animal wounded it with a blow that caused it to die.28With this explanation, the Rambam is clarifying the distinction Chulin 37a makes between an animal which is misukenet (dangerously ill) and trefe. The trefe condition is a result of wound, while in the case of a misukenet, all of its limbs and organs are sound. Nevertheless, as stated in Hilchot Trefot 5:2, there are other physical conditions which render an animal trefe even if it has not been attacked by an animal. These conditions were communicated as halachot to Moses at Sinai.

הלכה יב
אַף עַל פִּי שֶׁהִיא מֻתֶּרֶת גְּדוֹלֵי הַחֲכָמִים לֹא הָיוּ אוֹכְלִין מִבְּהֵמָה שֶׁמְּמַהֲרִין וְשׁוֹחֲטִין אוֹתָהּ כְּדֵי שֶׁלֹּא תָּמוּת וְאַף עַל פִּי שֶׁפִּרְכְּסָה בְּסוֹף שְׁחִיטָה. וְדָבָר זֶה אֵין בּוֹ אִסּוּר אֶלָּא כָּל הָרוֹצֶה לְהַחֲמִיר עַל עַצְמוֹ בְּדָבָר זֶה הֲרֵי זֶה מְשֻׁבָּח:
כסף משנה
12.
Although it is permitted, the great sages would not partake [of the meat] of an animal which people were hurrying to slaughter before it died.29The Maggid Mishneh (based on Chullin 37b) interprets this as a gesture of pious conduct. Note, however, Siftei Cohen 17:8. [This applies] even if it makes convulsive movements after being slaughtered.30Such a convulsive movement is a sign that it was alive at the time that it was slaughtered, as the Rambam continues to explain in the following halachah. This is a matter that does not involve a prohibition. Nevertheless, whoever desires to accept this stringency upon himself is praiseworthy.31The Maggid Mishneh quotes opinions that maintain that this leniency was granted only to alleviate the financial loss a Jewish owner of an animal would suffer. Therefore, meat from an animal belonging to a gentile which is in such a condition should not be eaten. The Shulchan Aruch (Yoreh De'ah 116:7) quotes this ruling.

הלכה יג
הַשּׁוֹחֵט בְּהֵמָה חַיָּה וְעוֹף וְלֹא יָצָא מֵהֶן דָּם הֲרֵי אֵלּוּ מֻתָּרִין וְאֵין אוֹמְרִין שֶׁמָּא מֵתִים הָיוּ. וְכֵן הַשּׁוֹחֵט אֶת הַבְּרִיאָה וְלֹא פִּרְכְּסָה הֲרֵי זוֹ מֻתֶּרֶת. אֲבָל הַמְסֻכֶּנֶת וְהִיא כָּל שֶׁמַּעֲמִידִין אוֹתָהּ וְאֵינָהּ עוֹמֶדֶת אַף עַל פִּי שֶׁהִיא אוֹכֶלֶת מַאֲכַל בְּרִיאוֹת אִם שְׁחָטָהּ וְלֹא פִּרְכְּסָה כְּלָל הֲרֵי זוֹ נְבֵלָה וְלוֹקִין עָלֶיהָ. וְאִם פִּרְכְּסָה הֲרֵי זוֹ מֻתֶּרֶת. וְצָרִיךְ שֶׁיִּהְיֶה הַפִּרְכּוּס בְּסוֹף הַשְּׁחִיטָה. אֲבָל בִּתְחִלָּתָהּ אֵינוֹ מוֹעִיל:
כסף משנה
13.
When a person slaughters a domesticated animal, wild beast, or fowl and blood does not flow out from them, they are permitted. We do not say: perhaps they were dead already. Similarly, when one slaughters a healthy animal and it does not make convulsive movements, it is permitted.
Different [rules apply with regard to an animal that] is dangerously ill, i.e., one which cannot maintain itself when others cause it to stand it up.32It must be able to stand up on its own when called or hit with a switch. If it is stood up by hand, it is still considered dangerously ill even if it is able to remain standing [Rama (Yoreh De'ah 17:1); Siftei Cohen 17:1]. [It is placed in this category] even if it eats the food of healthy animals. If [such an animal] is slaughtered and does not make any convulsive movements at all, it is a nevelah33I.e., we assume that it died before the slaughter was completed (see Chulin 38a). and one is liable for lashes [for partaking] of it. If it makes convulsive movements, it is permitted.
The convulsive movements must be made at the end of the slaughter. If they are made at the beginning, they are of no consequence.

הלכה יד
כֵּיצַד הוּא הַפִּרְכּוּס בִּבְהֵמָה דַּקָּה וּבְחַיָּה גַּסָּה וְדַקָּה. בֵּין שֶׁפָּשְׁטָה יָדָהּ וְהֶחֱזִירָה אוֹ שֶׁפָּשְׁטָה רַגְלָהּ אַף עַל פִּי שֶׁלֹּא הֶחֱזִירָה אוֹ שֶׁכְּפָפָה רַגְלָהּ בִּלְבַד הֲרֵי זֶה פִּרְכּוּס וּמֻתָּר. אֲבָל אִם פָּשְׁטָה יָדָהּ וְלֹא הֶחֱזִירָתָהּ הֲרֵי זוֹ אֲסוּרָה שֶׁאֵין זוֹ אֶלָּא הוֹצָאַת נֶפֶשׁ בִּלְבַד. וּבִבְהֵמָה גַּסָּה אֶחָד הַיָּד וְאֶחָד הָרֶגֶל בֵּין שֶׁפָּשְׁטָה וְלֹא כָּפְפָה בֵּין כָּפְפָה וְלֹא פָּשְׁטָה הֲרֵי זוֹ פִּרְכּוּס וּמֻתֶּרֶת. וְאִם לֹא פָּשְׁטָה לֹא יָד וְלֹא רֶגֶל וְלֹא כָּפְפָה כְּלָל הֲרֵי זוֹ נְבֵלָה. וּבְעוֹף אֲפִלּוּ לֹא רִפְרֵף אֶלָּא בְּעֵינוֹ וְלֹא כִּשְׁכֵּשׁ אֶלָּא בִּזְנָבוֹ הֲרֵי זֶה פִּרְכּוּס:
כסף משנה
14.
What is meant by convulsive movements? For a small domesticated animal and for both a small and a large wild beast, the intent is that it extended its foreleg and returned it, extended its hind leg even though it did not return it, or merely bent its hind leg.34The Maggid Mishneh and the Siftei Cohen 17:4 quote opinions that rule that if a small domesticated animal's foreleg was extended and it bent it, that is sufficient to render it acceptable. This is considered a convulsive movement and [the animal] is permitted. If, however, it merely extended its foreleg and did not return it, it is forbidden. [This movement is] merely a result of the expiration of the soul.
With regard to a large domesticated animal, [more lenient laws apply]. If it either extended its foreleg or its hind leg without bending it or bent its foreleg or hind leg without extending it, it is considered as a convulsive movement and it is permitted. If, however, it neither extended or bent its foreleg or its hind leg at all, it is considered as a nevelah.
With regard to a fowl, even if it only blinked its eyelid35Note the Siftei Cohen 17:5 which quotes different versions of Chullin 38b that state that a fowl must move its wing. Winking its eyes is not sufficient. or swatted its tail, it is considered a convulsive movement.36The Maggid Mishneh (and the Turei Zahav 17:4 and the Siftei Cohen 17:6) quote opinions that maintain that swishing its tail is also sufficient for an animal to be considered as having made a convulsive movement.

הלכה טו
הַשּׁוֹחֵט אֶת הַמְסֻכֶּנֶת בַּלַּיְלָה וְלֹא יָדַע אִם פִּרְכְּסָה אוֹ לֹא פִּרְכְּסָה הֲרֵי זוֹ סְפֵק נְבֵלָה וַאֲסוּרָה:
כסף משנה
15.
When one slaughters an animal that is dangerously ill at night and does not know37I.e., because he cannot see. Needless to say, if the room is illuminated, this law does not apply. whether or not it made convulsive movements, it is forbidden, because of the possibility that it is a nevelah.38I.e., we follow the principle that when a doubt concerning a Scriptural prohibition is involved, we rule stringently.

הלכה טז
כָּל אִסּוּרִין שֶׁבַּתּוֹרָה אֵין מִצְטָרְפִין זֶה עִם זֶה חוּץ מֵאִסּוּרֵי נָזִיר כְּמוֹ שֶׁיִּתְבָּאֵר שָׁם. לְפִיכָךְ הַלּוֹקֵחַ מְעַט חֵלֶב וּמְעַט דָּם וּמְעַט בְּשַׂר בְּהֵמָה טְמֵאָה וּמְעַט בְּשַׂר נְבֵלָה וּמְעַט בְּשַׂר דָּג טָמֵא וּמְעַט בְּשַׂר עוֹף טָמֵא וְכַיּוֹצֵא בָּאֵלּוּ מִשְּׁאָר הָאִסּוּרִין וְצֵרֵף מִן הַכּל כְּזַיִת וַאֲכָלוֹ אֵינוֹ לוֹקֶה וְדִינוֹ כְּדִין אוֹכֵל חֲצִי שִׁעוּר:
כסף משנה
16.
None of the substances prohibited by the Torah can be combined with each other [to reach the minimum measure for which one is liable for lashes] with the exception of the prohibitions that apply to a nazarite, as explained in that source.39As stated in Hilchot Nazirut 5:3, although there are separate prohibitions against eating raisins, grape peels, grape seeds, and partaking of wine, if one combined all these substances together, one is liable. Therefore when a person takes a small amount of fat, a small amount of blood, a small amount of the meat of a non-kosher animal, a small amount of the meat of a nevelah, a small amount of the meat of a non-kosher fish, a small amount of the meat of a non-kosher fowl, or the like from other prohibited substances, although he collects an olive-sized portion from the entire mixture and partakes of it, he is not liable for lashes. He is bound by the laws that apply when one eats half the minimum measure [of a forbidden] substance.40In which instance, the prohibition is Scriptural in origin, but lashes are not given (Chapter 3, Halachah 6).
The Rambam's statements in this and the following halachah touch on an issue of general significance. Rabbi Meir (Avodah Zarah 66a) maintains that forbidden substances of different types can be combined together to make a person liable for lashes. The Sages differ and maintain that they cannot be combined, but instead are judged individually. If there is enough of the one substance to make one liable, he is liable. If not, he is exempt.
The principle stated in Halachot 18-19 is a correlory to these concepts. Since the forbidden substances are not combined with each other, but are instead considered as discrete entities, they help nullify each other, as explained there.

הלכה יז
כָּל הַנְּבֵלוֹת מִצְטָרְפוֹת זוֹ עִם זוֹ. וּנְבֵלָה מִצְטָרֶפֶת עִם טְרֵפָה. וְכֵן כָּל בְּהֵמָה וְחַיָּה הַטְּמֵאִים מִצְטָרְפִין זֶה עִם זֶה. אֲבָל בְּשַׂר נְבֵלָה עִם בְּשַׂר בְּהֵמָה טְמֵאָה אֵין מִצְטָרְפִין. כֵּיצַד. הַלּוֹקֵחַ מִנִּבְלַת הַשּׁוֹר וְנִבְלַת הַצְּבִי וְנִבְלַת הַתַּרְנְגוֹל וְקִבֵּץ מִן הַכּל כְּזַיִת בָּשָׂר וַאֲכָלוֹ לוֹקֶה. וְכֵן אִם קִבֵּץ חֲצִי זַיִת מִנִּבְלַת בְּהֵמָה טְהוֹרָה וַחֲצִי זַיִת מִן הַטְּרֵפָה אוֹ חֲצִי זַיִת מִבְּשַׂר נְבֵלָה וַחֲצִי זַיִת מִבָּשָׂר מִן הַחַי מִן הַטְּהוֹרָה וַאֲכָלוֹ לוֹקֶה. וְכֵן בְּשַׂר הַגָּמָל וְהַחֲזִיר וְהָאַרְנֶבֶת שֶׁקִּבֵּץ מִכֻּלָּם כְּזַיִת וַאֲכָלוֹ לוֹקֶה. אֲבָל אִם צֵרֵף חֲצִי זַיִת מִנִּבְלַת הַשּׁוֹר וַחֲצִי זַיִת מִבְּשַׂר הַגָּמָל אֵינָן מִצְטָרְפִין. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה. וְכֵן בְּהֵמָה טְמֵאָה וְעוֹף טָמֵא אוֹ דָּג טָמֵא אֵין בְּשַׂר שְׁנֵיהֶן מִצְטָרֵף. לְפִי שֶׁהֵן שְׁנֵי שֵׁמוֹת. שֶׁהֲרֵי כָּל אֶחָד מֵהֶן בְּלָאו בִּפְנֵי עַצְמוֹ כְּמוֹ שֶׁבֵּאַרְנוּ. אֲבָל כָּל הָעוֹפוֹת הַטְּמֵאִין מִצְטָרְפִין כְּמוֹ שֶׁמִּצְטָרְפִין כָּל בְּהֵמָה וְחַיָּה הַטְּמֵאִין. זֶה הַכְּלָל כָּל שֶׁאִסּוּרָן בְּלָאו אֶחָד מִצְטָרְפִין. בִּשְׁנֵי לָאוִין אֵין מִצְטָרְפִין. חוּץ מִנְּבֵלָה וּטְרֵפָה הוֹאִיל וְהַטְּרֵפָה תְּחִלַּת נְבֵלָה הִיא:
כסף משנה
17.
All [types of] nevelot may be combined together. A nevelah may be combined with a trefe. All the non-kosher animals and wild beasts may be combined with each other. But the meat of a nevelah and the meat of a non-kosher animal may not be combined.
What is implied? When one takes [some meat] from a nevelah of an ox, some from the nevelah of a deer, some from the nevelah of a chicken and combined it so that he has an olive-sized portion of meat, he is liable for lashes if he eats it. Similarly, if he collected half of an olive-sized portion from the nevelah of a kosher animal and half of an olive-sized portion from a trefe, or half of an olive-sized portion from the meat of a nevelah and half from meat taken from a living kosher animal,41For this is included in the prohibition against a trefe, as stated in Halachah 10. he is liable if he eats it. Similarly, if he collects an olive-sized portion [by combining] the meat of a camel, a pig, and a hare,42Although each one of these species is mentioned separately in the Torah, they are all included in the same prohibition. he is liable if he eats it.
If, by contrast, he takes half of an olive-sized portion of a nevelah of an ox and half an olive-sized portion of a camel [an eats it], they are not combined.43The Ra'avad mentions that this point is the subject of a difference of opinion among the Sages of the Talmud, seemingly implying that the opinion which maintains that they should be combined should be followed. The Maggid Mishneh justifies the Rambam's position. Similar principles apply in all analogous situations. Similarly, the meat of a non-kosher animal, fowl, or fish are not combined for they involve different prohibitions. For each one is forbidden by a separate negative commandment, as we explained.44See Chapter 2. Nevertheless, all the forbidden species of fowl can be combined as may all the forbidden species of domesticated animals and wild beasts.
This is the general principle: Whenever substances are included in the same prohibition, they may be combined. [If they are included] in two [separate] prohibitions, they are not combined. The [only] exceptions are a nevelah and a trefe. [The rationale is that] a trefe is the beginning of [an animal] becoming a nevelah.

הלכה יח
הָאוֹכֵל מִנְּבֵלָה וּטְרֵפָה אוֹ מִבְּהֵמָה וְחַיָּה הַטְּמֵאִים מִן הָעוֹר וּמִן הָעֲצָמוֹת וּמִן הַגִּידִים וּמִן הַקַּרְנַיִם וּמִן הַטְּלָפַיִם וּמִן הַצִּפָּרְנַיִם שֶׁל עוֹף מִמְּקוֹמוֹת שֶׁמְּבַצְבֵּץ מִשָּׁם הַדָּם כְּשֶׁיֵּחָתְכוּ וּמִן הַשִּׁלְיָא שֶׁלָּהֶן אַף עַל פִּי שֶׁהוּא אָסוּר הֲרֵי זֶה פָּטוּר מִפְּנֵי שֶׁאֵלּוּ אֵינָן רְאוּיִין לַאֲכִילָה וְאֵין מִצְטָרְפִין עִם הַבָּשָׂר לִכְזַיִת:
כסף משנה
18.
When a person eats the skin, the bones, the sinews,45Note the Rambam's Commentary to the Mishnah (Chulin 9:1) which interprets the Hebrew term giddim as also referring to veins, arteries, and nerves. the horns, or the hoofs46This applies even if the portions eaten were soft and blood spurts from them. of a nevelah, a trefe, or a non-kosher domesticated animal or wild beast, from the nails of a non-kosher fowl in the places where blood would spurt through when they are cut off, or from their placenta,47As stated in Halachah 5. although this is forbidden, he is not liable. [The rationale is that] they are not fit to be eaten. They cannot be combined with meat [in the measure of] an olive-sized portion.

הלכה יט
קֵיבַת הַנְּבֵלָה וְקֵיבַת הַטְּמֵאָה מֻתֶּרֶת מִפְּנֵי שֶׁהִיא כִּשְׁאָר טִנֹּפֶת שֶׁבַּגּוּף. וּלְפִיכָךְ מֻתָּר לְהַעֲמִיד הַגְּבִינָה בְּקֵיבַת שְׁחִיטַת הָעַכּוּ''ם וּבְקֵיבַת בְּהֵמָה וְחַיָּה טְמֵאָה. אֲבָל עוֹר הַקֵּבָה הֲרֵי הוּא כִּשְׁאָר הַמֵּעַיִם וְאָסוּר:
כסף משנה
19.
[Milk found in] the stomach of a nevelah and the stomach of a non-kosher animal48The Rambam does not distinguish between milk that has coagulated and milk that is fluid. For even if it is fluid, it is already considered as a waste product. (Kessef Mishneh). is permitted, for it is like other waste products of the body. Therefore, it is permitted to use [milk found in] the stomach of an animal slaughtered by a gentile or the stomach of a non-kosher domesticated animal or wild beast to cause cheese to solidify.49I.e., since the digestive juices from the animal's stomach have already mixed with this milk, it will be an effective catalyst to cause the large quantity of milk to curdle and harden into cheese. See also Chapter 3, Halachah 13, and Chapter 9, Halachah 15.
The Rama (Yoreh De'ah 81:6) differs and quotes Rabbenu Tam's opinion states that liquid milk found in the stomach of a forbidden species is forbidden. Moreover, at the outset, one should not use even dried milk found in the stomach of a non-kosher animal as a catalyst because of the impression it will create. After the fact, it is permitted.
The skin of the stomach, by contrast, is like the other digestive organs and is forbidden.

הלכה כ
עוֹר הַבָּא כְּנֶגֶד פָּנָיו שֶׁל חֲמוֹר מֻתָּר בַּאֲכִילָה מִפְּנֵי שֶׁהוּא כְּמוֹ הַפֶּרֶשׁ וּמֵי רַגְלַיִם שֶׁהֵן מֻתָּרִין. יֵשׁ עוֹרוֹת שֶׁהֵן כְּבָשָׂר וְהָאוֹכֵל מֵהֶן כְּזַיִת כְּאוֹכֵל מִן הַבָּשָׂר. וְהוּא כְּשֶׁיֹּאכַל אוֹתָן כְּשֶׁהֵן רַכִּים:
כסף משנה
20.
The placenta of a donkey50Our translation is based on the glosses of Rashi and Tosafot, Bechoros 7b. The Ra'avad differs with the Rambam's ruling and maintains that this placenta is forbidden. The Maggid Mishneh justifies the Rambam's ruling. is permitted to be eaten because it is like dung and urine which is permitted. There is skin which is considered like meat and one who partakes of an olive-sized portion is considered like one who eats an olive-sized portion of meat, provided one partakes of it when it is soft.51And not processed so that it becomes hard like leather.

הלכה כא
וְאֵלּוּ שֶׁעוֹרוֹתֵיהֶן כִּבְשָׂרָן. עוֹר הָאָדָם וְעוֹר הַחֲזִיר שֶׁל יִשּׁוּב וְעוֹר חֲטוֹטֶרֶת שֶׁל גָּמָל שֶׁלֹּא טָעֲנוּ עָלָיו מַשָּׂא מֵעוֹלָם וְלֹא הִגִּיעַ לְמַשָּׂא שֶׁעֲדַיִן הִיא רַכָּה וְעוֹר בֵּית הַבּשֶׁת וְעוֹר שֶׁתַּחַת הָאַלְיָה וְעוֹר הַשָּׁלִיל וְעוֹר הָאֲנָקָה וְהַכֹּחַ וְהַלְּטָאָה וְהַחֹמֶט. כָּל אֵלּוּ הָעוֹרוֹת כְּשֶׁהֵן רַכּוֹת הֲרֵי הֵן כְּבָשָׂר לְכָל דָּבָר בֵּין לְאִסּוּר אֲכִילָה בֵּין לְטֻמְאָה:
כסף משנה
21.
The following [types of] skins are considered like meat: the skin of a human, the skin of a domesticated pig,52That of a wild boar, by contrast, is too tough to be eaten. the skin of a camel's hump upon which a burden has never been loaded, [because] it has not reached the age [to serve as a beast] of burden, for then it is still soft, the skin of genital area, the skin that is below the tail, the skin of a fetus, the skin of the hedgehog, the chameleon, the lizard, the snail.53As mentioned in the notes to Chapter 2, Halachah 7, the names of these species are a matter of debate. When all of these skins are soft, they are considered like meat with regard to all matters, whether with regard to [liability54This addition is necessary, for there is a prohibition against partaking of any skin, as stated in Halachah 18. for] the prohibition against partaking of them or with regard to the laws of ritual purity.55For an olive-sized portion of the meat of a nevelah can convey ritual impurity, while a hide or a piece of leather that size does not.

הלכה כב
נֶאֱמַר בְּשׁוֹר הַנִּסְקָל (שמות כא כח) "וְלֹא יֵאָכֵל אֶת בְּשָׂרוֹ". וְהֵיאַךְ הָיָה אֶפְשָׁר לְאָכְלוֹ אַחַר שֶׁנִּסְקַל וַהֲרֵי הוּא נְבֵלָה. אֶלָּא לֹא בָּא הַכָּתוּב אֶלָּא לְהוֹדִיעֲךָ שֶׁכֵּיוָן שֶׁנִּגְמַר דִּינוֹ לִסְקִילָה נֶאֱסַר וְנַעֲשָׂה כִּבְהֵמָה טְמֵאָה. וְאִם קָדַם וּשְׁחָטוֹ שְׁחִיטָה כְּשֵׁרָה הֲרֵי זֶה אָסוּר בַּהֲנָיָה. וְאִם אָכַל מִבְּשָׂרוֹ כְּזַיִת לוֹקֶה. וְכֵן כְּשֶׁיִּסָּקֵל לֹא יִמָּכֵר וְלֹא יִתְּנֶנּוּ לִכְלָבִים וְלֹא לְעַכּוּ''ם לְכָךְ נֶאֱמַר לֹא יֵאָכֵל אֶת בְּשָׂרוֹ. וּפֶרֶשׁ שֶׁל שׁוֹר הַנִּסְקָל מֻתָּר בַּהֲנָאָה. נוֹדַע שֶׁהוּא פָּטוּר מִסְּקִילָה אַחַר שֶׁנִּגְמַר דִּינוֹ כְּגוֹן שֶׁהוּזְמוּ הָעֵדִים יֵצֵא וְיִרְעֶה בָּעֵדֶר. וְאִם נוֹדַע אַחַר שֶׁנִּסְקָל הֲרֵי זֶה מֻתָּר בַּהֲנָיָה:
כסף משנה
22.
With regard to an ox condemned to be stoned,56For goring a human being. See Hilchot Nizkei Mammon, ch. 10, which explains the pertinent laws. [Exodus 21:28] states: "Its meat shall not be eaten." Now, how could one think that it would be eaten after it was stoned to death, for it is a nevelah?57For it died without ritual slaughter. Instead, the Torah is coming to teach you that once it has been sentenced to execution by stoning, it becomes forbidden; it becomes like a non-kosher animal. [Even] if one hurried and slaughtered it in an acceptable manner [before it was executed], it is forbidden to benefit from it.58Sefer HaMitzvot (negative commandment 188) and Sefer HaChinuch (mitzvah 52) include this among the 613 mitzvot of the Torah.
Instead, the corpse of the executed animal should be buried (Hilchot Pesulei HaMukdashim 19:11).
If one eats an olive-sized portion of its meat, he is liable for lashes. And when it is executed by stoning, its [meat] should not be sold or given to the dogs or to a gentile, [as implied by the phrase]: "shall not be eaten."59As stated in Chapter 8, Halachah 15, unless there is a teaching that states otherwise, this phrase implies both a prohibition against eating and a prohibition against deriving benefit. It is permitted [to benefit from] the dung of an ox condemned to be stoned.60As stated in Hilchot Ishut 5:2, the rationale is that the dung is considered of negligible importance with regard to the ox itself. As implied by Halachah 20, the dung of an animal is not considered as part of the animal itself, nor is it included in the prohibitions applying to it.
If it is discovered that [a condemned ox] is not liable to be stoned after it was sentenced, e.g., the witnesses who testified against it were disqualified, it may be sent out to pasture with the herd. If this was discovered after it was executed, it is permitted to benefit from [its meat].

קדושה הלכות מאכלות אסורות פרק ד
Kedushah Ma`akhalos Assuros Chapter 4