The image below was created by Dr. Akiyoshi Kitaoka.  Believe it or not, the image is not animated.  Your eyes and your brain are making it move.  To test this, stare at one spot for a couple seconds and everything will stop moving.  Or look at the black center of each circle and it will stop moving.  But move your eyes to the next black center and the previous will appear to move after you take your eyes away from it!  Visit Dr Kitaoka's <a href="http://www.ritsumei.ac.jp/~akitaoka/index-e.html">website</a> for more illusions.

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<img src="/gif/rotsnake.gif">