OPTICAL ILLUSIONS

Look at the black dot in the middle of the picture. Now move your head backwards and forwards, it appears as though the outer and inner ring are moving in opposite directions. This is because the focal distance (from your eyes to the point) is changing, and you interpret the relative positions of the circles accordingly.

Look closely at this collection of blocks...
Can't see anything?
Try moving away from the monitor.. Suddenly it will all become clear!.