Literally the text says “any lie-er with an animal, dying he shall die.” New International Version has “Anyone who has sexual relations with an animal must be put to death.” Translator’s Old Testament calls it “sexual intercourse.” The emphatic “dying he shall die” is the same as in 21.12. (See the comment there.)

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .