
Knight fighting a Bonnacon
The Bonnacon, Bonacon, or Bonasus is an animal similar to a bison that has acidic dung that burns like fire, which appears in medieval bestiaries.
Description[]
According to bestiaries, it lives in Europe and Asia, and only sprays its dung when startled. The bonnacon has curled horns and a mane like a horse.
It is featured in the Aberdeen bestiary, and was described in Pliny The Elder's Naturalis Historia as: "There are reports of a wild animal in Paonia {Greece} called the bonasus which has the mane of a horse, 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, [604 m], contact with which scorches pursuers like a sort of fire."
It has not been sighted since the time of Pliny The Elder.
Explanation[]

A European bison, a possible explanation behind the Bonnacon
The legend may be based on the European bison (Bison bonasus), also known as the Wisent or Zubr, because the two animals are very similar.
In Popular Culture[]
The Bonnacon has been featured as a monster in Final Fantasy XI, and as a fightable enemy in La-Mulana.