Cud

The chewing of the cud is one of the two visible marks by which Israel was to sort beasts into clean and unclean. A creature must both part the hoof and chew the cud; either trait alone disqualifies the animal for the table.

The Twin Test

The Levitical law gives the rule and then walks the four borderline cases that satisfy one criterion but fail the other: "Whatever parts the hoof, and is clovenfooted, [and] chews the cud, among the beasts, that may you⁺ eat. Nevertheless these you⁺ will not eat of those that chew the cud, or of those that part the hoof: the camel, because he chews the cud but doesn't part the hoof, he is unclean to you⁺. And the coney, because he chews the cud but doesn't part the hoof, he is unclean to you⁺. And the hare, because she chews the cud but doesn't part the hoof, she is unclean to you⁺. And the swine, because he parts the hoof, and is clovenfooted, but doesn't chew the cud, he is unclean to you⁺. Of their flesh you⁺ will not eat, and their carcasses you⁺ will not touch; they are unclean to you⁺" (Lev 11:3-8).

The Test Restated

Deuteronomy gives the rule again, this time with a positive list of seven game animals before the four exceptions: "These are the beasts which you⁺ may eat: the ox, the sheep, and the goat, the hart, and the gazelle, and the roebuck, and the wild goat, and the pygarg, and the antelope, and the chamois. And every beast that parts the hoof, and has the hoof cloven in two, [and] chews the cud, among the beasts, that may you⁺ eat. Nevertheless these you⁺ will not eat of those that chew the cud, or of those that have the hoof cloven: the camel, and the hare, and the coney; because they chew the cud but part not the hoof, they are unclean to you⁺. And the swine, because he parts the hoof but chews not the cud, he is unclean to you⁺: of their flesh you⁺ will not eat, and their carcasses you⁺ will not touch" (Deut 14:3-8).

The two passages line up: camel, coney, and hare on the cud-chewing-without-cloven-hoof side; swine alone on the cloven-hoof-without-cud side. The cud is the second half of a paired test that no animal in those four lists can satisfy in full.