Chimps Attack
Couple had Chimp Moe. Chimp Moe bit off a person's finger. Couple sent Chimp Moe to sanctuary. Years Pass. Couple goes to visit Chimp Moe for Chimp Moe's Birthday. Chimp Moe's Chimp Friends attack couple:

The couple had brought Moe a cake and were standing outside his cage when Buddy and Ollie, two of four chimpanzees in the adjoining cage, attacked St. James Davis, Martarano said. Officials have not determined how the chimps got out of their enclosure, he said....
St. James Davis had severe facial injuries and would require extensive surgery in an attempt to reattach his nose, Dr. Maureen Martin of Kern Medical Center told KGET-TV of Bakersfield. His testicles and a foot also were severed, Kern County Sheriff's Cmdr. Hal Chealander told The Bakersfield Californian.

Wow - who knew chimps could be so vicious?