Parallel lines geometrical-optical illusion mug

The café wall illusion is a geometrical-optical illusion in which the parallel straight dividing lines between staggered rows with alternating black and white "bricks" appear to be sloped. It was first described under the name Kindergarten illusion in 1898 and re-discovered in 1973 by Richard Gregory. According to Gregory, this effect was observed by a member of his laboratory, Steve Simpson, in the tiles of the wall of a café at the bottom of St Michael's Hill, Bristol. In the construction of the optical illusion often each "brick" is surrounded by a layer of "mortar" intermediate between the dark and light colors of the "bricks". In the first attempt at its deconstruction, the illusion was ascribed largely to irradiation, the light spread from dark to bright zones in the retinal image, and the image disappears when black and white are replaced by different colors of the same brightness. But a component of the illusion remains even when all optical and retinal components are factored out. Contrast polarities seem to be the determining factor in the tilt's direction. [Source: Wikipedia] So, even though it does not like it, the lines are indeed parallel. The caption "Don't trust your eyes!" may be edited or even deleted.