An optical illusion shared in a viral tweet has sent social media users' minds racing.
The image, which shows a group of friends in a nightclub, was posted by Eleanor Bailey, 18, Daily Mail reports. "My sister's arm in this club photo looks about 6 feet long," Bailey tweeted. "I'm crying."
The teen's photo has since racked up retweets and likes from hundreds of other users, who see the same optical illusion -- because Bailey's sister and some of her friends are also wearing black, the girl's arm appears elongated behind her friends' backs.
Internet users were confused, and tried to figure out whose arm it was. One user even said that she had stared at the photo for "20 minutes" to try to figure it out.
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"I'm confused by this," tweeted one user.
"So am I," replied another. "I can't trace who owns the hand."
Bailey said she was surprised by the attention she got from the tweet, according to The Telegraph.
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"I got 100 likes on a tweet, this has never happened before," she wrote. "I'm shook."
Inside Science describes optical illusions as being akin to "your brain taking a shortcut," adding that the images can "fool our brains by taking advantage of these kinds of shortcuts."
One of the most notable optical illusions in recent memory came from a seemingly innocuous social media post with a photo of a dress -- the image sparked a debate regarding the color of the dress. Some thought the dress was blue and black, while others saw it as white and gold, reports The Washington Post.
"What happened was two of my close friends were actually getting married and the mother of the bride took a photo of the dress to send to her daughter," said Caitlin McNeill, who sings in the band Canach. "When my friend showed the dress to her fiance, they disagreed on the color."
"We discovered this photo of the dress for the bride and couldn't agree on the color," said McNeill's bandmate Alan McInnes. "After this, the whole wedding party was in a dispute over [its color.]"
After the wedding party couldn't agree on what color the dress was, a band member decided to post the image online, where it took on a new viral life of its own.
Numerous celebrities including Taylor Swift, Justin Bieber, Mindy Kaling and Ellen DeGeneres weighed in on the dress phenomenon.
The real answer behind the strange phenomenon was in the way that our brains process information from our eyes. Some element of the image reportedly causes people to ignore certain visual information about the dress's color.
"Our visual system is supposed to throw away information," said neuroscientist Jay Neitz.
"So people either discount the blue side, in which case they end up seeing white and gold, or discount the gold side, in which case they end up with blue and black," added Wellesley College's Bevil Conway.