"Rocky," the 320-kg brown (or grizzly) bear (Ursus arctos) which wrestled a human in the Will Farrell film "Semi-Pro," was in a routine training session when he killed his trainer with a single bit to the neck. The bear had no previous record of aggressive behavior, and the training facility had operated without incident since its founding in 1992. As Roy Horn (of Siegfried and Roy) found out in 2003, even the best trained of carnivores still has instincts the most conscientious trainers don't always understand. I've read of a hand-raised cougar which broke away from its handler to attack a stuffed deer (an animal the cougar had never even seen alive) in a diorama at the Denver Museum of Nature and Science.
Authorities have not decided whether Rocky must be put down.