For decades, winking has been synonymous with a come-on, a quick and "sexy" flirtation you can wordlessly employ to relay the message you're down to swap bodily fluids.

In fact, winking is so ubiquitously used as a flirtation, a humblebrag or an acknowledgement of a mutual secret, that it was the fourth most commonly used emoji on iOS in 2015. Fifty three percent of people who responded to a 2015 Singles in America study reported they use the ol' winky emoji to flirt, which was significantly higher than the more forward kissy face (27 percent) or the friendlier straight-up smiley face (38 percent).

But, when did this whole winking thing start? Who decided that closing one eye rapidly and repeatedly while you stare at another person was the ultimate symbol for "Fuck me, I'm sexually potent?"

There's no record of the first slick wink, although the origins of the word "wink" itself can be traced back a few centuries to the Old English verb wincian, which meant "closing one's eyes quickly." That verb later became the root of the modern-day "to wink."

But it wasn't until the '60s and '70s that researchers started to look into the phenomenon to see why people were turned to such mush by it.

Given that eyes are the medium through which we appreciate the physicality of people who turn us on, it's well-known that they respond in both voluntary and involuntary ways when we think someone or something is hot. This is what drove biopsychologist Eckhard Hess to found the practice of pupillometry, a.k.a the measurement of pupil diameter for psychological purposes. He discovered that when you look at something you that turns you on, your pupils dilate. Winking, he theorizes, simply draws attention to your dilated pupil.

Except the funny thing is, to really get the point across, you have to wink at near-conniption levels if you really want to make someone horny for you. In the book Love Signals: A Practical Field Guide to the Body Language of Courtship, Dr. David Givens, director of the Center for Nonverbal Studies, writes that "rapid eyeblink (or 'eyelash flutter') means you've raised the blinker's level of psychological arousal," so "faster blinking may reflect sexual excitement."

The longer you look into those dilated, seizure-like eyes, the better your chance of laying down the law as the mayor of Bone Town. Sorry — we meant building a lasting, trust-filled relationship.

Body language expert Patti Wood also hypothesizes that winking removes the threat from a sexual interaction, essentially conveying the message that the winker is a safe person to sexually caress.

"[Winking] is a way of softening of what could be considered threatening continued eye contact," she says in her book SNAP: Making the Most of First Impressions, Body Language, and Charisma. "I analyzed Santa's body language in The Night Before Christmas, [which says] 'a wink of his eye and a twist of his head,' and that's a softening, like saying 'I did just come down your chimney and into your house, but I'm harmless.'"

That makes total sense. If Santa just came down your chimey and blankly stared at you, it would probably be a lot more terrifying than if he closed on eye knowingly at you. Same thing goes in the real world. If you just stared at someone without cutting the intensity with a little light, playful eye twitching, said stare would be interpreted less as "You're cute" and more as "I'm going to roast your disembodied knees with heirloom potatoes under a the full moon tonight."

Body language expert and former FBI agent Joe Navarro backed up this assertion to Broadly, adding that, as humans, there are only a tiny handful of ways we can communicate non-verbally with each other from more than a few feet away. There's waving, smiling, and tilting your head, but none of those convey any sort of sexual, yet approachable undertone. Winking gets the job done because it's quick, under-the-radar and gently suggestive.

"Even in a crowded, loud room, the message gets through," he says.

"I think [a winky face] makes the information more light-hearted or inviting, which is part of early flirtatious banter," says Jeffery Hall, an associate professor of communication studies at the University of Kansas and and author of The Five Flirting Styles. "If people are using emoji winks in texting or through a server, perhaps they recognize that mediated social interaction has some inherent distance they want to bridge, like making eye contact across a bar or club. Maybe an emoji wink is used to close that distance [and] overcome the mediated break between two people and try to establish connection."

Yep; that semi-awkward eye closure is really nothing more that the mutual acknowledgement that there's something discreet going on between you and someone else.

Whether you can pull off that bodily function without looking like your seizure medication ran out is a whole different story.