Moving Dots Optical Illusion

Can you see how this optical illusion seems to move and shift?

See Another Random Optical Illusion

Scroll down for the explanation.

Most people will see this optical illusion move and shift if they look at it for a short while.

Explanation

Since we live in a three dimensional world, we try to convert a two dimensional object into a 3D one. In this optical illusion, we try to make sense of these 2D objects. The shading used in this drawing is completely incongruous. We try to lock onto a bit of the illustration that looks appropriately shaded but then find it disjointed with shading in other nearby areas. The eyes keep jumping around the drawing trying to map out a 3D solution that would make the shading illustration make sense, but it never seems to work.