Dolphins are extremely playful, but little is known about how they — and other marine mammals — communicate during playtime. New research shows that bottlenose dolphins (Tursiops truncates) use the ‘open mouth’ facial expression — analogous to a smile — to communicate during social play. The dolphins almost always use the facial expression when they are in their playmate’s field of view, and when playmates perceived a ‘smile,’ they responded in kind 33% of the time.
