There may be no game simpler than tag. To play, you need nothing but a few friends and some energy. In fact, tag is so easy to play that it reaches other primate species: Gorillas like to play, too. Marina Davila Ross and colleagues spent three years watching and filming gorilla colonies at Germany and Swiss zoos for a study now out in Biology Letters. They shot footage of 21 different young gorillas goofing around in a game that resembles human children playing tag.