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Slanted grids. Grids 1, 3, 4, and 6 are identical of shape. One obtains the impression that each of these grids is slanted differently. This phenomenon is known as the Leaning Tower illusion. Grid 5 is identical to the middle part of grid 2. The lines of grids 2 and 3 converge to a single vanishing point, as do the lines of grids 5 and 6. Grids 2 and 3 appear aligned but grids 5 and 6 do not.
