Here’s an unsolved mystery as old as time: blindfolded humans cannot walk straight. If you blindfold a person and tell them to walk straight, that person will quickly begin to walk in circles and not even know it! Says Robert Krulwich in an NPR report, “Humans, apparently, slip into circles when we can’t see an external focal point, like a mountain top, a sun, a moon. Without a corrective, our insides take over and there’s something inside us that won’t stay straight.” Though many scientists have attempted to figure out what exactly that something is, no one has cracked it just yet. Watch the fun animation describing the strange phenomenon in the video above.