Most people won’t admit it, but we size up other people's characters all the time. In fact, research suggests that it takes just 30 seconds to make up our minds about someone’s intelligence and personality (we make other assessments even faster) and that these evaluations are surprisingly accurate.

In one study, researchers showed participants short videos of different couples interacting, and participants were able to detect which individuals had cheated on their partners.

Image: Flickr user Holly Lay