Once the tweet was posted, the internet went absolutely crazy with comments and hilarious memes.
Then for some Twitter twitter users, it all became clear.
It's not the first illusion to drive the internet crazy.
In April, a British Twitter user shared a confounding video of his son's toy train tracks, which appeared to show one track growing and shrinking depending on where he placed it. This is called the Jastrow illusion and has to do with the way the brain interprets curved segments.
Since May, more than 7.5 million people have viewed this Imgur image of a couple hugging - mostly because their legs look impossibly (painfully?) intertwined. As commenters eventually figured out, the illusion springs from the design on the man's shorts. Wait for it...
This hurts my brain...
In July, a Facebook user in the Philippines posted a photo of a floral carpet and challenged viewers to find the camouflaged phone placed on it. (That was shared more than 20,000 times, and liked by about 155,000.) A hint: The phone's patterned case is very similar to that of the rug, but they don't perfectly match up.
- additional reporting by Washington Post