Optical illusions have a way of driving people crazy. No matter how much you try to avoid being “tricked,” your brain often interprets things in unexpected ways. One illusion now confusing the entire internet shows six girls sitting on a couch—yet only five pairs of legs are visible. How is that possible? According to the Queensland Brain Institute, an optical illusion happens “when our brain and eyes try to speak to each other in simple language but the interpretation gets mixed up.”

Our brains evolved to react quickly to movement for survival, so sometimes they misread what our eyes see. A viral Reddit post features the now-famous photo: six girls lined up on a couch, but only five sets of legs in view. At first glance, it looks as if one girl’s legs have completely disappeared, sparking endless debate online.

One Reddit user explained that the “missing” pair actually belongs to the second girl from the left. Her legs are perfectly aligned behind the legs of the girl on the far left, making them almost impossible to distinguish. Their similar jeans and positioning create the illusion of fewer legs.

Another user, ElMangosto, broke it down further: Girl #1 has her legs crossed. Girl #2’s torn knee and white sock help identify her single visible leg, which blends with Girl #1’s. Girls #2 and #3 are leaning, adding to the confusion. Once you follow the clues, the illusion becomes clearer—though still a fun brain teaser. Share this with your friends and see if they can spot the “missing” legs!