"This is an animal called the Yena [Hyena], which is accustomed to living in the sepulchres of the dead and devouring their bodies. Its nature is that at one moment it is masculine and at another moment feminine, and hence it is a dirty brute.

It is unable to turn round, except by a complete reversal of its body, because its spine is rigid and is all in one piece.

It frequents the sheepfolds of shepherds and walks round the houses of a night and studies the tone of voice of those inside with careful ear, for it is able to do imitations of the human voice. In order that it may prey upon men called out at night by this ruse, it copies the sound of human vomiting.

Such dogs as it has called out like this, it gobbles up with hypocritical sobs. And if by chance sporting dogs should cross its shadow while they are hunting it, they lose their voices and cannot give tongue.

This beast has a stone in its eye, also called a yena, which is believed to make a person able to foresee the future if he keeps it under his tongue. It is true that if a yena walks round any animal three times, the animal cannot move. For this reason they affirm that it has some sort of magic skill."

- "A Medieval Bestiary", Metropolitan Museum of Art, 1986 (text compiled from various sources, I think)

[full book at: http://resources.metmuseum.org/resources/metpublications/pdf/A_Medieval_Bestiary_The_Metropolitan_Museum_of_Art_Bulletin_v_44_no_1_Summer_1986.pdf ]