According to the Houston Zoo, this seemingly self-satisfied monkey has a good reason to "smile": He's uncovered the camera set up by a Borneo-based game reserve to spy on him.
"Looks like someone knew about the 'hidden' cameras," tweeted the zoo. Naturally, monkeys don't bare teeth to express joy or amusement, they do so to communicate anger.
Given that he's being spied on by a game reserve, I'd say he's earned the right to be pissed.
[Joe My God, photo via @houstonzoo]