not surprising. once a wild, always a wild. The attack happens because the wild animal goes insane if their needs are not met. That's why zoos try their best to recreate 100% identical environment for each species.
btw - biting testicle/fingers/face off is typical chimp attack. They did same to other chimp (invader) in wild because ripping testicle off is the symbol of victory and dominance. I happened to watch some chimp documentary in Animal Planet couple years ago. I was horrified. Chimp Attacks are brutal....
