How does the  brain work is still one of most intriguing unresolved mysteries of science.  Here is one practical test that will show you just how amazing and hard it is to evaluate how does the brain work. You need to look at the animation and tell if you see the dancer turning clockwise or anti-clockwise. You may think that it is clear that is is turning only way way. It turns out that different people have different perception of what is really happening.