The Bonnacon (also known as Bonasus) is a bull-like beast with a horses mane. It also has two horns that are curved inward. It protects itself by discharging foul fumes and a long trail of dung. This dung is so hot that it sets fire to and burns anything it comes in contact with. 

It has curled horns and when startled sprays acidic dung that burns on contact with skin "like a kind of fire". The legend may be based on a type of bison in reality. Some suggest that it had some resemblance to theEuropean bison, which went extinct in the wild in 1919. A supposed representation of it appears on the coat of arms belonging to the Hollingshead Family, possibly alluding to a legendary confrontation between one of their ancestors and this beast.

The animal was described by Pliny in his Naturalis Historia: "There are reports of a wild animal in Paionia called the bonasus, which has the mane of ahorse, but in all other respects resembles a bull; its horns are curved back in such a manner as to be of no use for fighting, and it is said that because of this it saves itself by running away, meanwhile emitting a trail of dung that sometimes covers a distance of as much as three furlongs, contact with which scorches pursuers like a sort of fire."