Two gorillas play a game. Researchers have found that young great apes tease others in their group: juvenile chimpanzees, bonobos, gorillas and orangutans have been seen pulling older animals’ hair, poking them, body-slamming them and waving objects repeatedly in front of their faces. If they didn’t get a reaction, the juveniles would step up their intrusive behaviour – a tactic that will be familiar to many human parents.