If a woman approaches any animal to mate with it, you must kill both the woman and the animal. They must surely be put to death; their blood is upon them.
Sins against the seventh commandment are here ordered to be severely punished. These are sins which, of all others, fools are most apt to make a mock at; but God would teach those the heinousness of the guilt by the extremity of the punishment that would not otherwise be taught it. I. Lying with another man's wife was made a capital crime.
Commenting on Leviticus 20:10-21
And if a woman approach unto any beast, and lie down thereto,.... In order that the beast may lie with her, and solicit it to commit such an action with her, see Lev 18:23, thou shall kill the woman and the beast: the woman by stoning, and the beast with clubs, as the Targum of Jonathan; and this for the same reasons as before, as...
If a woman approach unto any beast - We have the authority of one of the most eminent historians in the world, Herodotus, to say that this was a crime not unknown in Egypt; yea, that a case of this nature actually took place while he was there. Εγενετο δ' εν τῳ νο μῳ τουτῳ επ' εμευ τουτο το τερας, Γυναικι Τραγος εμισγετο αναφανδον. Τουτο ες επιδειξιν ανθρωπων απικετο.