Yawning is a mysterious thing. For starters, just reading that sentence may have caused you to yawn. The behavior, technically a reflex that involves opening the mouth and a simultaneous stretching of the eardrum, is contagious--and the video above sets out to explain why.
The video was created by VSAUCE, a YouTube channel that offers "Amazing Facts & The Best of the Internet." It starts by debunking various myths about yawning. We don't do it for lack of oxygen, and it doesn't just help equalize the pressure in our heads—the real medical reason is less obvious, but you'll have to watch the video to learn what it is. We'll give you a hint: research has shown that people yawn less when they have an icepack on their forehead.
We also learn about the function of pandiculation, or yawning and stretching simultaneously, and how animals that move in groups might have evolved such a mechanism. As the narrator puts it, yawning might well be "advantageously contagious."
But not everyone can benefit. One's tendency to catch other people's yawns may depend on empathy. Children with autism spectrum disorders—who tend to exhibit impaired empathy— also show less susceptibility to catching yawns.
The video is full of interesting facts about yawning, including why other animals use it to look intimidating, attract mates, or just realign their jaws after a big meal.
See more VSAUCE videos here.