Leviticus 11 gives its rule for land animals in a single compact formula: an animal may be eaten only if it parts the hoof, is cloven-footed, and chews the cud, and both conditions must hold together rather than either alone being sufficient. The text goes out of its way to name four specific animals that satisfy only one half of the rule and are therefore forbidden despite the partial match, the camel and the hare and the rock badger, which chew the cud but do not have a parted hoof, and the pig, which has a parted, cloven hoof but does not chew the cud, a level of explicit exception-naming that shows the criteria were being applied deliberately rather than simply describing whatever animals a particular community already happened to eat. Water creatures receive a parallel two-part rule, fins and scales together, which permits familiar fish while excluding shellfish, eels and other scaleless or finless water animals regardless of how commonly they were eaten elsewhere in the ancient Near East.
Birds, by contrast, receive no stated rule at all, only a list of about twenty forbidden species named individually, eagle, vulture, kite, raven, ostrich, owl, hawk, cormorant, stork, heron, hoopoe and bat among them, a list scholars have long noted groups fairly consistently around birds of prey, scavengers and birds associated with carrion or with wetlands, even though the text itself never states that association as the underlying rule the way it states the cud-and-hoof rule for land animals.