Hullin, Chapter Three, Mishnah One
Exodus 22:30 states, Meat in a field that is terefah you shall not eat, cast it to the dogs. The word terefah literally means torn apart by animals. The rabbis assume that since another verse already forbade eating nevelah, which they interpret to mean any animal that was improperly slaughtered, the word terefah must refer to something else. They therefore interpret the word terefah to refer to an animal that have suffered an injury, or has some sort of defect, that will cause it to die imminently. Such an animal is prohibited even if it was slaughtered properly.
The first five mishnayot of our chapter deal with which wounds or defects cause an animal to be a terefah. Our mishnah lists 18 different ways a cattle can become a terefah.
The following [defects] render cattle terefah:
1) If the esophagus was pierced;
2) If the windpipe severed;
3) If the membrane of the brain was pierced;
4) If the heart was pierced as far as its cavity thereof;
5) If the spine was broken and the cord severed;
6) If the liver was gone and none of it remained;
7) If the lung was pierced,
8) Or if part of it was missing
a) Rabbi Shimon says: only if it was pierced as far as the main bronchi;
9) If the stomach,
10) If the gall-bladder was pierced,
11) If the intestines were pierced;
12) If the innermost stomach was pierced,
13) If the greater part of the outer stomach was pierced.
a) Rabbi Judah says: in a large animal [if it was torn] to the extent of a handbreadth, and in a small animal the greater part.
14) If the omasum (the third stomach of a ruminant) [was pierced];
15) Of if the second stomach was pierced on the outside;
16) If the animal fell from the roof;
17) If most of its ribs were fractured;
18) Or if it was mauled by a wolf
a) Rabbi Judah says: small animals [are terefah] if mauled by a wolf, large cattle if mauled by a lion; small fowl if mauled by a hawk, large fowl if mauled by a falcon.
19) This is the rule: if an animal with a similar defect could not continue to live, it is terefah.
Sections 1-18: This is the list of the 18 defects that cause cattle, cows, sheep and goats, to become a terefah. Most of these are self-explanatory, more so perhaps to those of you that are biologists or veterinarians. Rabbi Shimon and Rabbi Judah (in sections 8, 13 and 18) distinguish between large animals (cows) and small animals (sheep and goats). According to these two sages, the defects are not exactly the same for the two different types of animals.
Section nineteen: This section provides the general rule of when an animal becomes a terefah.