Q: Why is yawning contagious?
A: People yawn when the pressure between their ears is different from that of the outside pressure. The yawning pops the ears and thus balances the inside and outside pressure. Because of the balancing there is a perceptible drop or increase in the surrounding room pressure. And if at this moment there is another person present in the vicinity of the yawning person, this change in room pressure will cause him to yawn to balance his in-between-ear pressure to that of the room pressure. Thus the cycle goes on till the inside-ear-pressure of all the persons and that of the room pressure is equal. But since every time someone yawns, there is a change in room pressure causing some one else to yawn, the cycle never ends... UNLESS all the people in the room yawn at the same time. Since the probability of all the people yawning at the same time is very low, the yawning goes on and on, leading us to believe that yawning is contagious.
Yawning is an orgasm for your face.