Yawning is the simultaneous inhalation of air, accompanied by the widening of the mouth followed by the exhalation of breath and best served up with a big vocalization. It is a peculiar behaviour with no obvious function. Theories about excess build up of carbon dioxide turned out to be wrong and so it is not clear why we do it. Moreover, yawning is one of those contagious behaviours such as laughing that trigger the same behaviour in others. Interestingly, contagious yawning in not that common in young children and those with autism spectrum disorder have been reported not to show contagious yawning. So yawning is a peculiar behaviour, triggered by a number of possible situations and seems to have some cultural component linked to automatic empathy.
But I bet we would all be yawning more if we were being treated for depression with Clomipramine. This antidepressant produces an unusual side effect in about 1 in 20 patients who experience an orgasm while yawning. Now that’s one side effect that I doubt the drug companies are going to be sued for. After all we have all thought about it during a boring lecture when we feel the need to yawn.