The examples of play mentioned so far generally relate to an animal's gaining experience in its relationship with its environment, and with its own physical abilities. However, playfulness also allows juveniles to learn how to deal with fellow group members. Social play, the fourth and final category, may facilitate cooperation, develop alliances, and encourage innovation in social behavioral patterns. Young animals from across the mammalian spectrum engage their peers in bouts of wrestling and other physical activities. Elephants slap and wrestle each other with their trunks.
Giraffes use their long necks to spar gently, necko a necko .
Moose calves may practice their head-butting on unsuspecting trees when a peer is unavailable. Researchers suggest that social play may safely teach young the skills they will later use in aggressive social competition. However, such play may also simultaneously strengthen social bonds between group members, a process that serves to limit the amount of actual aggression between group members. Animals, it turns out, communicate playful intentions with certain stereotyped signals. The most widespread play signal is the play face, a relaxed, open-mouth expression seen in many mammal species, used virtually from birth.