Perspective Optical Illusion

Are these boxes all the same size?

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Yes, they are.

Explanation

Yep, they really are exactly the same size. Hard to believe, isn't it? This optical illusion takes advantage of a three dimensional technique where all of the lines meet at one point off the edge of the canvas, thus making the mind see the picture as a 3D model of reality, rather than just lines on a screen. Since the right box appears to be the farthest away, our mind adjusts the size and sees it as the largest.