Meilah 16a

לֹא שָׁנוּ אֶלָּא לְעִנְיַן טוּמְאָה, אֲבָל לְעִנְיַן אֲכִילָה – טְהוֹרִין בִּפְנֵי עַצְמָן, וּטְמֵאִים בִּפְנֵי עַצְמָן. וְלֵוִי אָמַר: אֲפִילּוּ לַאֲכִילָה נָמֵי מִצְטָרְפִין.

The mishna taught that all carcasses join together, which indicates that carcasses of non-kosher animals join together with carcasses of kosher animals, only with regard to ritual impurity. But with regard to the prohibition of eating animal carcasses, kosher animal carcasses are distinct, i.e., they join together only with other kosher animals, and non-kosher animal carcasses are likewise distinct. And Levi says: Even with regard to the prohibition of eating animal carcasses, kosher and non-kosher carcasses join together.

וְרַב אַסִּי אָמַר: טְהוֹרִים לְעַצְמָן וּטְמֵאִין לְעַצְמָן. אִיכָּא דְאָמְרִי: פְּלִיגָא אַדְּרַב, וְאִיכָּא דְאָמְרִי: לָא פְּלִיגָא.

And Rav Asi says: Kosher animal carcasses are distinct, and non-kosher animal carcasses are distinct. Since Rav Asi did not specify whether he is referring only to eating or also to ritual impurity, there are those who say that Rav Asi disagrees with the opinion of Rav, i.e., he interprets the mishna as referring to all carcasses of a similar kind, that is, from kosher animals on the one hand, and from non-kosher animals on the other hand. And there are those who say that Rav Asi does not disagree with the opinion of Rav, and concedes that kosher and non-kosher animal carcasses join together with regard to ritual impurity.

מֵיתִיבִי: מִיתַת פָּרָה, וְחַיֵּי גָמָל – אֵין מִצְטָרְפִין זֶה עִם זֶה. הָא מִיתַת שְׁנֵיהֶם – מִצְטָרְפִין, וְקַשְׁיָא לְרַב אַסִּי!

The Gemara raises an objection against the first explanation of the opinion of Rav Asi from a baraita : With regard to half an olive-bulk from the carcass of a dead cow and half an olive-bulk from the flesh of a live camel, they do not join together with one another. It can be inferred from here that if both of them are dead, they do join together. Rav can explain this baraita as referring to ritual impurity, but this poses a difficulty to Rav Asi.

אֵימָא: הָא חַיֵּי שְׁנֵיהֶם – מִצְטָרְפִין, וּמַנִּי – רַבִּי יְהוּדָה הִיא, דְּאָמַר: אֵבֶר מִן הַחַי נוֹהֵג בַּטְּמֵאָה.

The Gemara answers: One should say that the correct inference from the baraita is not that if both of them, the cow and the camel, are dead, then they join together. Rather, one should infer that if both of them are alive, they join together. And who is the tanna of the baraita ? It is Rabbi Yehuda, who said: The prohibition of eating a limb from a living animal applies even to the limb of a non-kosher animal.

אֲבָל מִיתַת שְׁנֵיהֶם, מַאי? לָא מִצְטָרְפִי? אִם כֵּן, מַאי אִירְיָא דְּרָהֵיט וְתָנֵי ״מִיתַת פָּרָה וְחַיֵּי גָמָל״, הָא אֲפִילּוּ מִיתַת שְׁנֵיהֶם לָא מִצְטָרְפִי!

The Gemara raises a difficulty with this answer. But in that case, what is the halakha if both of them, the cow and the camel, are dead? Do they not join together? If so, why does the tanna run specifically to an extreme case and teach: Half an olive-bulk from the carcass of a dead cow and half an olive-bulk from the flesh of a live camel? After all, even if both of them are dead, they do not join together.

וְעוֹד, תַּנְיָא: חֲצִי זַיִת פָּרָה בְּחַיֶּיהָ וַחֲצִי זַיִת גָּמָל בְּמִיתָתָהּ – אֵין מִצְטָרְפִין. אֲבָל חֲצִי זַיִת מִפָּרָה וַחֲצִי זַיִת מִגָּמָל, בֵּין בְּחַיֶּיהָ בֵּין בְּמִיתָתָהּ – מִצְטָרְפִין. קַשְׁיָא רֵישָׁא אַסֵּיפָא! אֶלָּא לָאו שְׁמַע מִינַּהּ: מִיתַת שְׁנֵיהֶם – מִצְטָרְפִין!?

And furthermore, it is taught in a baraita : Half an olive-bulk from the flesh of a cow when it is alive and half an olive-bulk from the carcass of a camel when it is dead do not join together; but half an olive-bulk from a cow and half an olive-bulk from a camel, whether alive or dead, do join together. The first clause in the baraita is difficult as it is apparently contradicted by the latter clause. Rather, isn’t it correct to conclude from the baraita that if there is half an olive-bulk from each of the two of them when they are dead, they join together?

אָמַר לְךָ רַב אַסִּי: הַאי תַּנָּא סָבַר אִיסּוּר חָל עַל אִיסּוּר.

The Gemara answers: Rav Asi could have said to you that this tanna holds that a prohibition takes effect even where another prohibition already exists. He maintains that the prohibition of eating an animal carcass takes effect even with regard to the flesh of a non-kosher animal, which is already prohibited, and for this reason the two half olive-bulks join together, as the same prohibition against eating an animal carcass applies to both. By contrast, Rav Asi himself maintains that a prohibition does not take effect where another prohibition already exists, and therefore this baraita does not pose a difficulty to his opinion that the two do not combine.