They say seeing is believing, but our eyes have a habit of tricking us. In fact, it happens more often than most of us even realize. For example, did you ever notice that there’s a figure eight nestled inside the eight of diamonds in a regular deck of cards? Now that we’ve pointed it out to you, you’ll probably think about it every time you play a card game from now on!

The image below is just as sneaky, but is designed that way to test our eyes for something known as curvature blindness. Before we get into what that means exactly, go ahead and take a look:

Do you see wavy lines in the white and black areas, but alternating zig-zags and waves in the gray middle area? If so, you’ve just diagnosed yourself with curvature blindness. Don’t worry, it’s not an actual medical condition you need to see a doctor about or seek any treatment for. The optical illusion was created by Kohske Takahashi, PhD, from Kyoto University in Japan. Believe it or not, the graphic features identical wavy lines throughout the entire image. The study from 2017 shows how this “blindness” comes from our brains being triggered by the conflicting information our eyes are giving them. While speaking with the Telegraph, Dr. Takahashi explained his theory behind this observation: “I’d say that our eyes and brain may have been evolutionarily adapted to detect corners more efficiently than curves. We are surrounded by artificial products, which have much more corners than the natural environment does, and hence our visual.”

Our brains might also interpret the gray colors as shadows rather than solid parts of the lines. Whatever the reason is, it can be difficult to tear your eyes away from the image when you realize how it’s deceiving you — especially the areas that blend the seemingly zig-zag lines on gray background back into the wavy appearance on white and black. No matter how long you stare at it, though, you’ll probably always see the same illusion. Luckily, learning most of us have curvature blindness isn’t anything to worry about. If it was, it would have caused a lot of problems long before Takahashi unlocked this surprising way our brains work. Instead, it’s just a fun anecdote you can share with your friends.

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