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Why Do We Laugh When We're Tickled?

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It's a mystery that's challenged some of science's greatest minds, including Charles Darwin, Galileo, Francis Bacon, and Plato [PDF]. One thing is for sure: It’s not because we find it funny. In fact, many people find tickling very unpleasant. So why does it make us laugh?

There are two kinds of tickling phenomena: Gargalesis, the heavy tickling that produces laughter, especially by targeting sensitive areas like the armpits and stomach; and knismesis, which is caused by light movement and tends to elicit an itching sensation rather than laughter. You can't tickle yourself because your brain knows it's coming.

When the nerve endings in your epidermis are stimulated by a light touch, they send a signal through the nervous system to your brain. Using functional magnetic resonance imaging machines (fMRI), researchers have determined that two areas of the brain create that tickle sensation: the somatosensory cortex, the area responsible for analyzing touch, and the anterior cingulated cortex, which is involved in creating pleasurable feelings.

Another fMRI study has shown that both laughing at a joke and laughing while being tickled activate an area of the brain called the Rolandic Operculum, which controls facial movements and vocal and emotional reactions. But tickling laughter also activates the hypothalamus, the area of the brain that regulates the fight or flight response—and fires when you’re anticipating pain. This has led some scientists to believe that laughing when you’re tickled could be a natural signal of submission to an aggressor, which would reduce the duration of any attack. It also explains why we may laugh at just the threat of being tickled.

Robert Provine, neuroscientist at the University of Maryland, Baltimore County and author of the 2000 book Laughter: A Scientific Investigation, says that laughter during tickling creates bonds between babies and parents. “When people say they hate being tickled and there’s no reason for it, they forget that it’s one of the first avenues of communication between mothers and babies,” he told Slate. “You have the mother and baby engaged in this kind of primal, neurologically programmed interaction.”

We're not the only animals that laugh when we're tickled: Great apes giggle, and so do rats.

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Big Questions
What Are Curlers Yelling About?
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Curling is a sport that prides itself on civility—in fact, one of its key tenets is known as the “Spirit of Curling,” a term that illustrates the respect that the athletes have for both their own teammates and their opponents. But if you’re one of the millions of people who get absorbed by the sport once every four years, you probably noticed one quirk that is decidedly uncivilized: the yelling.

Watch any curling match and you’ll hear skips—or captains—on both sides barking and shouting as the 42-pound stone rumbles down the ice. This isn’t trash talk; it’s strategy. And, of course, curlers have their own jargon, so while their screams won’t make a whole lot of sense to the uninitiated, they could decide whether or not a team will have a spot on the podium once these Olympics are over.

For instance, when you hear a skip shouting “Whoa!” it means he or she needs their teammates to stop sweeping. Shouting “Hard!” means the others need to start sweeping faster. If that’s still not getting the job done, yelling “Hurry hard!” will likely drive the point home: pick up the intensity and sweep with downward pressure. A "Clean!" yell means put a brush on the ice but apply no pressure. This will clear the ice so the stone can glide more easily.

There's no regulation for the shouts, though—curler Erika Brown says she shouts “Right off!” and “Whoa!” to get her teammates to stop sweeping. And when it's time for the team to start sweeping, you might hear "Yes!" or "Sweep!" or "Get on it!" The actual terminology isn't as important as how the phrase is shouted. Curling is a sport predicated on feel, and it’s often the volume and urgency in the skip’s voice (and what shade of red they’re turning) that’s the most important aspect of the shouting.

If you need any more reason to make curling your favorite winter sport, once all that yelling is over and a winner is declared, it's not uncommon for both teams to go out for a round of drinks afterwards (with the winners picking up the tab, obviously). Find out how you can pick up a brush and learn the ins and outs of curling with our beginner's guide.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Why You Should Never Take Your Shoes Off On an Airplane
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What should be worn during takeoff?

Tony Luna:

If you are a frequent flyer, you may often notice that some passengers like to kick off their shoes the moment they've settled down into their seats.

As an ex-flight attendant, I'm here to tell you that it is a dangerous thing to do. Why?

Besides stinking up the whole cabin, footwear is essential during an airplane emergency, even though it is not part of the flight safety information.

During an emergency, all sorts of debris and unpleasant ground surfaces will block your way toward the exit, as well as outside the aircraft. If your feet aren't properly covered, you'll have a hard time making your way to safety.

Imagine destroying your bare feet as you run down the aisle covered with broken glass, fires, and metal shards. Kind of like John McClane in Die Hard, but worse. Ouch!

Bruce Willis stars in 'Die Hard' (1988)
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A mere couple of seconds delay during an emergency evacuation can be a matter of life and death, especially in an enclosed environment. Not to mention the entire aircraft will likely be engulfed in panic and chaos.

So, the next time you go on a plane trip, please keep your shoes on during takeoff, even if it is uncomfortable.

You can slip on a pair of bathroom slippers if you really need to let your toes breathe. They're pretty useless in a real emergency evacuation, but at least they're better than going barefoot.

This post originally appeared on Quora. Click here to view.

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