Mishnayos Taharos Perek 1 Mishnah 4

The hide, meat juice, sediment, dried-up meat, bones, sinews, horns and hooves join together [to make up the minimum quantity in order] to convey food-uncleanness, but not to [make up the minimum quantity in order to] convey nevelah-uncleanness. Similarly, if a man slaughtered an unclean animal for a Gentile and it still has convulsions, it can convey food-uncleanness, but it conveys nevelah-uncleanness only after it is dead, or its head has been chopped off. [Scripture] has [thus] made more cases that convey food-uncleanness than those that convey nevelah-uncleanness.

וּבַבְּהֵמָה, הָעוֹר וְהָרֹטֶב וְהַקִּפָּה וְהָאֲלָל וְהָעֲצָמוֹת וְהַגִּידִים וְהַקַּרְנַיִם וְהַטְּלָפַיִם, מִצְטָרְפִין לְטַמֵּא טֻמְאַת אֳכָלִין, אֲבָל לֹא טֻמְאַת נְבֵלוֹת. כַּיּוֹצֵא בוֹ, הַשּׁוֹחֵט בְּהֵמָה טְמֵאָה לְנָכְרִי וְהִיא מְפַרְכֶּסֶת, מְטַמְּאָה טֻמְאַת אֳכָלִין, אֲבָל לֹא טֻמְאַת נְבֵלוֹת, עַד שֶׁתָּמוּת אוֹ עַד שֶׁיַּתִּיז אֶת רֹאשָׁהּ. רִבָּה לְטַמֵּא טֻמְאַת אֳכָלִין, מִמַּה שֶּׁרִבָּה לְטַמֵּא טֻמְאַת נְבֵלוֹת: