Not every smile was created equal. And not every smile is genuine either. There are tight smiles, forced smiles, and awkward smiles, but they aren't the kinds of smiles we are really hoping to see. The most sincere kind of smile is known as the Duchenne smile, which involves contraction of both the major muscles that raise the mouth and the cheeks which forms crow's feet around the eyes.

Can you spot the fake smile in the video below: