A Buzzfeed Blue optical illusions video (see below) has challenged the minds of more than 5 million people.

According to Optics4Kids, optical illusions are images that trick our brains into seeing things that aren’t really there through the clever use of color, light and patterns.
The five optical illusions in the BuzzFeed clip test how you see colors, stripes, bars and even Tom Cruise. Though they are all interesting brain teasers, one optical illusion in the clip is really stumping people.

It’s shown near the end of the video and features a spinning target tunnel. After you focus on the target tunnel, you are supposed to look at your hands. Your hands are suppose to stretch. The trick worked for some people.

KaylaBird, a YouTube user who got it to work, wrote, “The last one when I looked at my hand, I said, "Oh dear God, what have you done to meh?!" I was legit freaking out xD.”
It didn’t work for Skeletal Scarab though, who wrote in the video's comments, “'Now look at your hands' OH MY GOD they look the same as normal.”

Michael Bach, a professor of Functional vision research and electrophysiology at the University of Freiburg in Baden-Württemberg, Germany, wrote on his personal website that optical illusions show us how wonderful our brains are at adaptation. 

"Optical illusion sounds pejorative, as if exposing a malfunction of the visual system," he wrote. "Rather, I view these phenomena as highlighting particular good adaptations of our visual system to experience with standard viewing situations. These experiences are based on normal visual experiences, and thus under unusual contexts can lead to inappropriate interpretations of a visual scene."

Bach also said that if you can’t see optical illusions, you’re not the only one.

“Don’t let it irk you if you don’t see all the phenomena described. For many illusions, there is a percentage of people with perfectly normal vision who just don’t see it, often for reasons currently unknown.”