Albert Barnes Commentary Exodus 21:28-32

"And if an ox gore a man or a woman to death, the ox shall be surely stoned, and its flesh shall not be eaten; but the owner of the ox shall be quit. But if the ox was wont to gore in time past, and it hath been testified to its owner, and he hath not kept it in, but it hath killed a man or a woman, the ox shall be stoned, and its owner also shall be put to death. If there be laid on him a ransom, then he shall give for the redemption of his life whatsoever is laid upon him. Whether it have gored a son, or have gored a daughter, according to this judgment shall it be done unto him. If the ox gore a man-servant or a maid-servant, there shall be given unto their master thirty shekels of silver, and the ox shall be stoned." — Exodus 21:28-32 (ASV)

The animal was slain as a tribute to the sanctity of human life (compare the marginal references and Genesis 4:11). It was stoned, and its flesh was treated as carrion. Guilty negligence on the part of its owner was reckoned a capital offense, to be commuted for a fine.

In the case of a slave, the payment was the standard price of a slave, thirty shekels of silver. See Leviticus 25:44-46; Leviticus 27:3, and the marginal references for the New Testament application of this fact.