Hullin, Chapter Three, Mishnah Three
Todays mishnah lists what defects render a bird a terefah.
The following [defects] render birds terefah:
1) If the esophagus was pierced,
2) If the windpipe was severed;
3) If a weasel struck [the bird] on the head in such a place as would render it terefah.
4) If the gizzard was pierced
5) If the intestines were pierced.
6) If it fell into the fire and its innards were scorched:
a) If they turned green, it is invalid,
b) But if they remained red it is valid.
7) If one trod upon it or knocked it against a wall or if an animal trampled upon it, and it still jerks its limbs, and it remained alive after this for twenty-four hours, and it was thereafter slaughtered, it is valid.
Sections 1-2: These are the same signs that render cattle terefot.
Section three: If a weasel (or any other animal) strikes the bird on a spot on its head in such a manner that we would need be concerned that the brain membrane was pierced, then it is a terefah.
Section six: If the innards turn green (gangrene?), that is a sign that the bird is going to die. If they remain red, the color that they were before the bird was burned, then the bird is not a terefah.
Section seven: If after having been struck in some manner the bird begins to jerk its limbs, it must live for another twenty-four hours before we can be sure that it would not have died from the blow. If it is slaughtered before 24 hours are up, then the bird is a terefah.