“We’re just playing” is such an important message, it turns out, that many species have developed their own vocabulary for it.25 Dogs, for example, have a “play bow”—forearms extended, head down, hindquarters in the air—which they use to initiate a bout of play.26 Chimps use an open-mouthed “play face,” similar to a human smile,27 or double over and peer between their legs at their play partners.28 And many animals, in addition to using specific gestures, will also move slowly or engage in exaggerated or unnecessary movement, as if to convey playful intent by conspicuously wasted effort that
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