Early zoology courtesy of The Aberdeen Bestiary (1100s, England), University of Aberdeen Library; accession number: MS 24. Special Collections Centre, Bedford Road, Aberdeen, Scotland, United Kingdom.
There is an animal called the beaver, which is extremely gentle; its testicles are highly suitable for medicine. Physiologus says of it that, when it knows that a hunter is pursuing it, it bites off its testicles and throws them in the hunter's face and, taking flight, escapes. But if, once again, another hunter is in pursuit, the beaver rears up and displays its sexual organs. When the hunter sees that it lacks testicles, he leaves it alone. Thus every man who heeds God's commandment and wishes to live chastely should cut off all his vices and shameless acts, and cast them from him into the face of the devil.