Why are some monkeys so humorous?

Research indicates that many mammals, including monkeys and other primates, have developed senses of humor. Apes have been observed both in captivity and in the wild to play and play tricks on each other with physical responses that are similar to human laughter.

Most primates have two forms of laughter: a silent, teeth bared reaction that research indicates is equivalent to a human smile and a panting laugh-like sound that they use during play and at other times to indicate that all activity is in good fun. There is a documented incident of a gorilla in Woodside, California playing a joke on her trainer. After tying together the trainer's shoelaces, she moved away and gave the sign for chase.