2,583. Water Fowl

Hilchos Shechita 10:6

Similar to the previous halacha, if the greater part of the height and circumference of a skull is crushed, the animal’s a treifa even if the membrane remains intact and the skull isn’t missing any pieces. If the greater part of its height was crushed but the greater part of its circumference was intact, or vice versa, there’s a doubt as to the animal’s status; the Rambam is inclined to prohibit such an animal.

Hilchos Shechita 10:7

Regarding water fowl like geese, if the bones of the skull are punctured, the bird is treif even if the membrane isn’t punctured; this is because its membrane is soft. If a weasel struck a bird of the land on the head, or if such a bird was struck by stone or wood, we put a hand near the hole and apply pressure, or we put a hand in the bird’s mouth and push up. If the bird’s brain comes out through the hole, we know that the membrane was punctured and the bird’s a treifa. If such is not the case, the bird remains permitted.