Yawning is one of the great mysteries of life. You see someone yawn, and you feel like yawning yourself. You get tired, you yawn, presumably because you need more oxygen in the brain. You are bored by an Internet article, you yawn (and click away). But what really is yawning? There hasn’t been a very conclusive answer yet, but scientists have found a surprising link between the length of a yawn and the size of the brain.