Toharot, Chapter One, Mishnah Four
This entire mishnah, save for the first word, can be found in Hullin 9:1. After having explained the rules governing the purity/impurity of the carrion of clean and unclean birds, the mishnah discusses cattle, meaning large herd animals (sheep, goats and cows).
1) 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.
2) 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.
3) [Scripture] has [thus] made more cases that convey food-uncleanness than those that convey nevelah-uncleanness.
Section one: These are all parts of the animal that are not generally or ever eaten. However, these parts, joing together with the generally edible parts of the animal to create a minimum volume the size of an egg to convey uncleanness to other foods if the animal was rendered unclean. The reason is that all although these parts are not eaten on their own, they are sometimes eaten with other parts of the meat. Alternatively, some of these things protect the meat of the animal, even if they themselves are not eaten. Therefore, they join with the meat in adding up to this minimum value.
However, these things do not join together with the rest of the meat to cause nevelah-uncleanness, which requires the minimum volume of an olive.
Section two: This animal cannot be eaten by a Jew or by a Gentile. It cant be eaten by a Jew because it is an unclean animal, for instance a camel. It cant be eaten by a Gentile because it is still convulsing and is therefore prohibited under the Noahide prohibition of eating the limb of a living animal. Nevertheless, this animal is considered food because just as when a Jew slaughters a kosher (clean) animal he causes it to be able to receive impurity, so too when he slaughters a non-kosher animal, he causes it to be able to receive impurity. However, it is not considered a nevelah in order to convey nevelah uncleanness until it is truly dead or has its head cut off. If its head is cut off, it is considered dead even if it is still convulsing.
Section three: The mishnah closes by noting there are more cases where something conveys food-uncleanness than nevelah uncleanness.