This is a cool optical illusion, based on persistence of vision. (Thanks to Emily.)
Follow these instructions:
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Relax and concentrate on the four small dots in the middle of the picture below for about 30-40 seconds.
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Close your eyes, or look at a wall near you (any smooth, single colored surface should do).
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You will see a circle of light developing.
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What do you see? Moreover, who do you see?
