I picked up this link from Manon Eileen (@manon_eileen) on Twitter, and it's a fun one: a study has been done to see whether people engage reflexively, that is automatically, in staring contests. The result? People with a dominance motive will indeed engage in a staring match with an angry face without even thinking about it. People with other motives will gaze on other types of faces longer. Here's the link.