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Very nice demo! Contrast reversals of the squares and their edges at different times make a huge difference.

The two rows of squares are moving to the right at the same speed; however, the top row appears to be moving to the right, while the bottom one appears to be moving to the left. 上下の正方形の列は等速度で右に動いていますが、上の列は右に、下の列は左に動いているように見えます。