An optical illusion photo of a cat recently caused frenzy over social media. The photo puzzled the viewers who couldn’t decide whether the cat was going up or down a set of stairs. Behavioral Science professor Nick Chater of the Warwick Business School in the U.K. recently explained to CNET why our eyes can deceive us while looking at a photo. Nick Chater said that while we are able to see 3D, our eyes are only able to receive 2D images.

“This seems puzzling, because it can be shown mathematically that there is an implied number of 3D scenes that will create the same 2D images. Most of the time, our brain is spectacularly good at solving this problem. It usually turns out that precisely one 3D interpretation is ‘sensible’ and all the others are bizarre, in one way or another.”

Chater stated that the while looking at the photo of the cat, if someone sees the cat coming downstairs, the gray square at the top of the photo could be interpreted as the ceiling. This makes an acute 45-degree angle that is aligned with the staircase. If someone sees the cat going upstairs, the gray square is now being interpreted as the floor. This makes an obtuse 135-degree angle within the staircase.

The puzzling photo of the cat going up or down the stairs will continue to cause problems simply because it’s all based on how our eyes are able to interpret certain lines, shapes and colors within an image. So, what exactly is the verdict on the photo? Chater said there isn’t a right or wrong answer.

“If we could only tell the ‘slant’ of the mysterious square patch in relation to the staircase, we would know if it was floor or ceiling, and so there would be no ambiguity. But the image cleverly leaves the gray square bereft of any clues. So we flip from one interpretation to the other.”

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