Do dolphins smile? Yes, according to this study

Bottlenose dolphins use the ‘open mouth’ facial expression – analogous to a smile – to communicate during social play, researchers say. — AFP

Some pet owners are convinced they’ve seen their dog or cat smile, but it’s unlikely to be the case.

Experts in the field can’t say whether animals can smile or not. However, researchers from France and Italy claim to have observed this behaviour in dolphins.