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.

Related on HuffPost:

GALLERY: SLEEP QUOTES EXPLAINED With Dr. Michael Decker, American Academy of Sleep Medicine
Loading Slideshow...
  • "You snooze, you lose."

    This saying also harkens back to viewing sleep as wasted time. Yes, there are times when if you were to snooze you could lose, says Maas, like if you're behind the wheel of a car. But in general, if you <em>don't</em> snooze, you lose, he says. "If sleep is unnecessary, it's the biggest mistake evolution ever made." But there's another way to think about it, in light of recent reserach linking sleep and obesity. As HuffPost Healthy Living <a href="http://www.huffingtonpost.com/2012/05/01/sleep-obesity-genes-fat_n_1465483.html" target="_hplink">reported earlier this month</a>: <blockquote>"The longer you sleep, the less important genetics become in determining what you weigh," explained Dr. Nathaniel Watson, co-director of the University of Washington Sleep Disorders Center. "Does this mean you can sleep yourself thin?" Watson asked. "Probably not. But you can sleep yourself to a point where environmental factors, like diet and activity, are more important in determining your body weight than genetics."</blockquote>

  • "Early to bed, early to rise, makes a man healthy, wealthy and wise." - Benjamin Franklin

    "If you go to bed early and get the right amount of sleep, that enhances your health," explains Decker, as it allows for adequate time for restorative, deep sleep. Getting enough sleep will also guarantee <a href="http://www.huffingtonpost.com/2012/03/12/sleep-deprivation-productivity-harvard_n_1334877.html" target="_hplink">a more productive day</a>, which in turn could lead to wealth. And "short sleep can impair decision making and memories, so the better we sleep the better cognitive function is," he says. Looks like Franklin was right!

  • "I need my beauty sleep."

    There is some truth in the idea of <a href="http://www.bmj.com/content/341/bmj.c6614.full?sid=f12d1b75-86cc-4bed-a06b-9ebc4f337b05" target="_hplink">waking up prettier</a>, according to a 2010 study published in the <em>British Medical Journal</em>. Researchers photographed people after a good night's sleep and after a period of sleep deprivation, then asked respondants to rate the photos on health, attractiveness and tiredness. The photos of sleep-deprived people received lower scores across the board. It may be partially due to the fact that while asleep, your body goes to work <a href="http://www.huffingtonpost.com/2012/01/25/beauty-sleep-skin_n_1229259.html" target="_hplink">repairing and healing things like skin cells</a>, YouBeauty reported, and not getting enough sleep can lead to early signs of aging, says Decker. People who say they need beauty sleep are right to recognize the fact that they look and feel better after a night's rest, he says.

  • "I slept like a baby."

    "Babies and children spend much more time in <a href="http://www.huffingtonpost.com/2012/02/27/sleep-stages-what-happens-during-sleep_n_1297941.html" target="_hplink">slow-wave sleep</a> than adults," explains Decker. That's the stage when "the brain is least responsive to external stimulation," he says. So sleeping like a baby -- as long as it's for seven to nine hours, rather than all day like a newborn -- is a sleep goal to aspire to. "It's being able to sleep and be completely undisturbed regardless of what's happening in the environment," he says. Sounds good to us!

  • "Sleep, those little slices of death; Oh how I loathe them." - Edgar Allan Poe

    "It gets back to this idea that we're not productive when we're sleeping," says Decker, that sleep is wasted or lost time. "Many people try to avoid sleep to get more out of life, and in fact in doing so they're probably shortening their lifespan." "We know that sleep deprivation causes irritability, anxiety, weight gain, depression, and contributes to a high risk of hypertension, diabetes, stroke," says Maas. "To not value sleep is to not value life."

  • "Sleep tight!"

    The saying "sleep tight, don't let the bed bugs bite" may date back to the days of the Plague, says Decker, but no matter its origins, is simply a wish of good sleep today. Maas offers another explanation: Soldiers who had to take shifts sleeping in hammocks had to adjust the ropes tying their portable beds to nearby trees or walls, he says, especially if a heavier soldier was due for a rest.

  • "Even where sleep is concerned, too much is a bad thing." - Homer

    As much as we'd like to be able to recommend sleeping until you can't sleep anymore, it is possible to overdo it on the zzz's. In fact, the <a href="http://www.journalsleep.org/ViewAbstract.aspx?pid=27780" target="_hplink">same study</a> that found short sleep to point to an earlier death found similar results for people who regularly slept nine or 10 hours a night when their bodies would be just fine on seven. And, like sleeping less than six hours a night, sleeping more than eight hours a night is also <a href="http://www.huffingtonpost.com/2012/03/27/sleep-heart-problems-too-much-too-little_n_1380730.html" target="_hplink">linked to an increased risk of heart problems</a>, according to a March study. <br><br> While some people are genetically longer sleepers, Decker says, long sleep can also be a sign that there's something wrong, like sleep apnea. For those people, nighttime sleep "is so disruptive, they need to sleep longer to try to compensate for interruptions that occur during the night," he says.

  • "A good laugh and a long sleep are the best cures in the doctor's book." - Irish Proverb

    This feel-good saying is sort of like prescribing "Take two Aspirin and call me in the morning," says Decker. But there is <em>some</em> truth to it. "Sleep restores body and brain cells, we absolutely know that," says Maas. "Sleep is absolutely critical to health and well-being, the evidence is overwhelming."

  • "Sleep before midnight is what counts."

    Night-owls can relax; this one's a myth -- as long as you're still meeting your nightly sleep requirements, says Maas. It's not <em>when</em> you go to sleep but going to sleep (and waking up) around the same time every day that really makes a difference, he explains.