Let me share an interesting find originally titled “This Optical Trick Is Annoying the Hell Out of Me” by Gizmodo. I had this animation on my hard for a while, but before I learnt how to reduce it’s size to a minimum (while at the same time being able to retain decent quality of the .gif file), I refrained myself from sharing it on this site (and widgets).
So, what is really going on here? What you see at first is a floating shape whose corners are covered with a yellow post-its. Your brain immediately recognises it as a rectangle, as it tries to connect the shape with something already familiar. But see what happens when the yellow stickers are removed from the animation. The actual shape of the floating object is revealed – in reality resembling nothing close to the rectangle you thought you were seeing at first. How amazing was that?