Step 1 - Place a small square of cardboard or paper on a bright red or green backround.
Step 2 - Cover both the square and the backroundwith to or three sheets of wax paper or one piece of tissue paper.
Step 3 - Gaze at the gray square.
Step 4 - If the backround is red, the square takes on the color blue-green and if the backround is green the square appears redish.
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