Optical illusions have a way of making us question what we see. No matter how hard you try to avoid being fooled, your brain often interprets images in unexpected ways. A new illusion taking over the 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 occurs “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, which sometimes leads to misreading what’s right in front of us.

The viral Reddit photo features six girls lined up on a couch, but only five sets of legs appear. At first glance, it looks like one girl’s legs have completely vanished, sparking a wave of online debate.

One Reddit user suggested that the “missing” legs belong to the second girl from the left. Her legs line up almost perfectly behind the legs of the girl on the far left, making them nearly impossible to distinguish. Their similar jeans and posture blend together, creating the illusion.....