Many species interact in the wild, most often as predator and prey. But recent encounters between humpback whales and bottlenose dolphins reveal a playful side to interspecies interaction. In two different locations in Hawaii, scientists watched as dolphins "rode" the heads of whales: the whales lifted the dolphins up and out of the water, and then the dolphins slid back down. The two species seemed to cooperate in the activity, and neither displayed signs of aggression or distress. Whales and dolphins in Hawaiian waters often interact, but playful social activity such as this is extremely rare between species.