Shake Your Head!

Carefully, though, don't hurt yourself!  If you shake your head side-to-side while staring at the picture at right, it becomes more obvious what the picture is showing. 
I've noticed a similar phenomenon when looking through window screens, or (better yet) picket fences.  It's a terrific example of how your brain puts assembles information gathered over time...

This isn't really an illusion in the usual sense, but more a demonstration of the brain's contribution to perception...

Via friend and reader Simon M...