From Malcolm Gladwell’s The Tipping Point:
Yawning is incredibly contagious. I made some of you reading this yawn simply by writing the word “yawn”. The people who yawned when they saw you yawn, meanwhile, were infected by the sight of you yawning–which is a second kind of contagion. They might even have yawned if they only heard you yawn, because yawning is also aurally contagious: if you play an audio-tape of a yawn to blind people, they’ll yawn too. And finally, if you yawned as you read this, did the thought cross your mind–however unconsciously and fleetingly–that you might be tired? I suspect that for some of you it did, which means that yawns can also be emotionally contagious.
Did you yawn?