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Pandiculation - A stretching and stiffening of the trunk and extremities, as when fatigued and drowsy or on waking, often accompanied by yawning.
What better topic for a morning open thread (on an otherwise unremarkable day) than an article about yawning?
It is so that humans and many animals yawn reflexively, and no one really knows why. There are a lot of proposed theories, plenty of experiments have been done, and scientists remain stumped. Adding to the dumbfounded scientists' chagrin at being uncharacteristically dumbfounded, experiments have proven that yawning is contagious. Try it sometime in a group of people: fake a yawn, and see how many others follow.
Yawning is very often accompanied by the stretching of the muscles of the extremities, chest and back, like this kitty here is pictured doing. That the act of stretching and yawning has its very own word is telling as to how important and ubiquitous it is, even if our white coat donning, slide-rule wielding heroes can't figure out the purpose of the whole yawning and stretching business.
One theory that seems to have some observational support is that animals pandiculate to prepare for, or in anticipation of, sudden exertion. It has some support in an evolutionary sense as well for social animals where a single alert member of a group may infect all the rest with his or her yawn-virus. It has been seen in the wild that animals will yawn and/or stretch even when in the midst of a life-threatening stand-off, such as a Cheetah defending her cubs from a Lion.
This, however, is thought to be more of a warning signal than anything else. A wide open mouth with lots of big sharp teeth is certainly something to be wary of. It is not an aggressive display, but a defensive one, as if to say, "Hey, Mr. Predator, I have lots of big, sharp teeth too, so if you try to hurt me, you might get hurt too."
In that way, yawning seems to be a sort of universal communication. We all know that the person clutching their own neck is probably choking. We also know that the person or animal yawning at us is isn't interested in a fight. Or much of anything else having to do with us, for that matter.
The reason yawning is such a contagious act is also a big mystery, though various hypotheses are floated frequently. Animals in social groups may yawn, infecting others of said social group with the yawning disease, in order to synchronize sleep patterns. One of the more interesting bits is that yawning's contagiousness is not limited to same-species social groups. You, too, can make your dog yawn. Just do it first.
The contagiousness of the act, though, has been shown empirically to be related to the empathetic connection between the individuals the infection passes between. As Wikipedia notes,
As with other measures of empathy, the rate of contagion was found to be greatest in response to kin, then friends, then acquaintances, and lastly strangers. Related individuals (r≥0.25) showed the greatest contagion, in terms of both occurrence of yawning and frequency of yawns. Strangers and acquaintances showed a longer delay in the yawn response (latency) compared to friends and kin. Hence, yawn contagion appears to be primarily driven by the emotional closeness between individuals.
So it makes some sense that brothers-from-another-mother-of-a-completely-different-species can and do catch our yawn-itis. They are family, whether hairless, feathered or furred.
Also, I guess, scaled.
I don't think fish yawn, though.
Oops.