I'm not exactly sure where to put this...
In the movie The Shawshank Redemption there is an instance in which the prison rapists try to force the main character into having oral sex with them, threatening to stab him in the head is he tries to bite their genitalias off. He then responds that injuries to the brain causes the victim to bite, and bite very, very hard.
I wonder, is this true? If so, is it true if other body parts than the brain are injured?