Do you know:

Why human yawn? Most research suggest that the lack of oxygen in our brain or the lack of fresh air causes a person to yawn. Well, that was true at some points. However, recent research has proven that yawning is coordinated to the social behaviour of a group. This means that when a person yawn in a bus, other people will start yawning very soon. This may be due to the human ability of detecting and responding to other people's yawns.