When filmmaker David Farrier came across an ad from Jane O’Brien Media calling for young male fitness models to be restrained and tickled on camera, he felt compelled to find out what on Earth was behind that casting call. Pushing past the production company’s vitriolic resistance to “association with a homosexual journalist,” he created and recently premiered the Sundance documentary "Tickled," which sheds light on the sport of “competitive endurance tickling.”

Yup, you heard us right: Competitive endurance tickling is a thing. O’Brien’s ad insists it’s a "completely athletic activity," though the notice also requests “attractive, ticklish and masculine guys.”

You’ll have to watch the documentary to learn whether this spectacle is a genuine display of sportsmanship or a form of tickle porn (which is a real genre to be googled at your own risk). Who can say? Maybe competitive endurance tickling is in the eye of the beholder.

But equally fascinating — and perhaps more easily researchable — are the reasons why people tickle one another in everyday life. After all, most of us have tickled someone or been tickled at some point — even if we don't turn it into a competitive sport. Why does tickling happen in the first place?

The dictionary definition of “tickle” is “lightly touch or prod (a person or a part of the body) in a way that causes itching and often laughter.” Perhaps revealingly, the verb also means “appeal to (someone's taste, sense of humor, curiosity, etc.).”

The dominant image of tickling in many of our minds involves children teasing their friends or extorting their siblings. Since this reflects many of our childhood memories, tickling can seem inherently sadistic. But according to University of Maryland neuroscientist Robert Provine, author of Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond, most people experience tickling positively when it’s consensual. "If you look at children, if you tickle them, they run away, but they typically come back," he observes.

According to studies by Provine, people rate being tickled ambivalently at a 5 on a 10-point scale from very unpleasant to very pleasant, with tickling someone else at a 5.9.

The reasons we play this game are totally different from why we're ticklish in the first place, though. The tickle response, like the startle response, is a mechanism our brains use to distinguish between touching and being touched, which is why we can't tickle or surprise ourselves. "Tickling involves the neurological program for the generation of self and other," Provine explained.

We need these instincts so we don't get alarmed whenever we brush against a wall or our own clothing, he added. "What would your life be like if, every time you bumped into something, you would startle yourself? Everyone would be really goofy."

As with many evolutionary traits, though, people have exploited ticklishness for social purposes. In this case, showing affection and getting attention are the top reasons Provine's subjects have cited for tickling.

Even those who swear they detest the sensation usually make one exception — and it’s more like hot-and-heavy competitive endurance tickling than many would care to admit.

"I hate being tickled, but in bed with my boyfriend, it's okay" was a common survey response among women, said Provine. So was, "I had a date with a guy I really liked. He was just sitting there, and to get the physical ball rolling, I tickled him and then he tickled me back."

Here’s another curious finding: People engage in tickling about 10 times less often after age 40, which Provine chalks up partially to "a decline of sexual activity at that time.” On top of that, people tickle members of the opposite sex six times as often as the same sex. Some respondents even confided that their erogenous zones are ticklish.

Apparently, nothing sparks romance like a tickle war.

"It binds people together in a give and take of physical play" from a young age, Provine explained. "It also binds people together in sexual activities. Amongst adults, the tickle battle becomes sexual foreplay."

Of course, sex isn't the only reason we dart our hands over companions' skin. Parents and grandparents tickle kids to bond with them, and it’s true that children taunt one another in such a manner. In fact, Provine said, the reason so many of us dislike the act is that we grew up with siblings forcing it on us. But when voluntary, it becomes a friendly game. As Randy Newman sang, “What can you do to amuse me? . . . Why don’t you tickle me?”

So, the silly pastime just got either a lot more philosophical or a lot more R-rated, depending how you look at it. Competitive endurance tickling may be a fringe fad, but tickling itself serves far too many purposes to evaporate anytime soon.

Suzannah Weiss is a New York-based writer with degrees in Gender and Sexuality Studies, Modern Culture and Media, and Cognitive Neuroscience from Brown University.

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