Why is it when someone else yawns, you yawn to

even hearing someone yawn triggers me yawning??

Adelie penguins, for instance, employ yawning as part of their courtship ritual. The happy couples face off amid the ice floes and the males engage in what is described as an "ecstatic display," their beaks open wide and their faces pointed skyward.

It may be, therefore, that when your entry upon the scene inspires a round of uncontrollable yawning, you have merely stumbled onto a gaggle of Adelie penguins in disguise, who are signaling their powerful erotic longing for you. A slim hope, admittedly, but any port in a storm.

As for the larger question of why yawns are catching, nobody really knows. Fact is, we don't know why people yawn, period.

It was long believed you yawned when there was too much carbon dioxide and not enough oxygen in your blood. A part of your brain called the brain stem detected this and triggered the yawn reflex. Your mouth stretched wide and you inhaled deeply, shooting a jolt of oxygen into the lungs and thence to the bloodstream.

Subsequently, you exhaled a lot of CO2. Often you'd stretch while yawning, which seemed to temporarily improve circulation. You yawned and stretched a lot more when you got tired because your breathing slowed down.

Or so people thought. In recent years, though, a few radicals have said the preceding is all malarkey. Who knows, they say, maybe we yawn because it's too warm in the room.