Other than the sloth, whose smile is pretty much permanently attached, the non-human animal most associated with smiling is the bottlenose dolphin. But somewhat like the sloth, the dolphin’s smile is just a feature of the way its mouth turns up at the sides. A dolphin that appears to be smiling at you when it bobs up beside your boat might not be thinking, “Hey, let’s be friends!” even though it’s difficult for humans to interpret that delightful expression any other way.
But if dolphins aren’t smiling at us, they may be smiling at each other — or at least doing something very similar. Researchers in Italy and France found that dolphins are more likely to display an expression that looks like a human smile (what the researchers called an “open mouth facial display”) when they’re playing with other dolphins.
However, the authors point out that the expression could also be used defensively. Even when they’re playing, a dolphin’s smile might not mean what a smile means to humans.
