A Bonacon is an heraldic monster with the appearance of a bull. However, it has small horns curled in like a ram's, a horse's tail and a mane. The head of a Bonacon appears in English heraldry at least twice. In 1560, it was granted to Richard Candelor of Walsingham in Norfolk, and a Bonacon's head was also granted to Hugh Hollynside of Cheshire in 1561. This beast was also known to Aristotle and Pliny, and features in the Mappa Mundi in Hereford Cathedral.

It is generally assumed that the Bonacon is not commonly seen in heraldry, as the creature's most unique feature is the manner in which it defends itself. Upon being pursued, it raises it's tail and emits such a noxious gas that trees within three acres catch fire. The enthusiasm of any pursuer would be dampened by this powerful emission. The bonacon is normally depicted standing on all fours with it's tail raised and the emission radiating.