Chullin, Chapter 3, Mishnah 5. The chapter has been mapping the boundary between treifah and kosher: the earlier mishnayot listed the physical defects that render an animal a treifah, and then the conditions that look alarming but leave the animal fit. Our mishnah continues on that second side of the line, and it does so with a striking category: illnesses and poisonings that may well kill the animal, yet still do not make it a treifah.
The Principle Behind the List
The logic to keep in mind throughout: treifah status depends on actual structural damage to one of the organs the halachah identifies. A condition can be serious, even fatal, and still not qualify, because nothing inside the animal has been perforated, torn, removed or destroyed. Sickness alone is not treifah.
The Cases
"Achuzat hadam" - an animal suffering from a rush or congestion of blood, with the result that breathing becomes difficult for it.
"Ve'hame'ushenet" - an animal that inhaled smoke from a fire and is likewise struggling to breathe.
"Ve'hametzunenet" - an animal that caught a chill and became ill from it.
"Ve'she'achlah hardufni" - an animal that ate oleander, a plant that is toxic to animals.
"Ve'she'achlah tzo'at tarnegolim" - an animal that consumed chicken droppings, also poisonous to animals.
"O sheshatah mayim ra'im" - literally, or the animal drank harmful water. The reference is to water left standing exposed, where a snake could have come and left venom behind in it.
In every one of these cases the mishnah rules "kesheirah" - the animal is kosher. It may be sick, it may even be dying, but the ailment or the toxin has not inflicted the kind of internal damage that creates a treifah.
Kosher and Also Safe
These animals are not merely permitted in the technical sense; they are safe to eat. When an animal ingests a substance that is poisonous to animals, that does not make its meat dangerous to a human being. Oleander and chicken droppings harm livestock, not people. As for the suspect water, the animal's digestion transforms the venom so that it no longer poses a threat to whoever eats the meat.
When the Poison Still Threatens a Person
The mishnah now turns to a case that ends differently. "Achlah sam hamavet" - the animal swallowed a deadly poison, the kind that threatens human beings as well; "o shehikichah nachash" - or a snake struck it. The ruling: "muteret mishum treifah" - from the standpoint of treifah law there is nothing to object to, since no organ within the animal was injured. But "va'asurah mishum sakanat nefashot" - the animal is off limits because of the risk to life. Whoever ate it could be killed by that poison or by that venom.
Here the prohibition comes from a different direction entirely. Because the meat is genuinely harmful to the one eating it, the halachah forbids it, even though the treifah rules would have allowed it.
Note the contrast with the earlier case. There the water had been contaminated by venom that a snake left behind, and the animal's digestive process neutralized it. Here the snake bit the animal directly, and that venom retains its potency even after the animal has processed it. For that reason the meat may not be eaten.