Psychology
Three Pac-Man shapes are enough to make your brain draw a triangle that isn't there
Psychologist Gaetano Kanizsa arranged three wedge-cut circles so their gaps lined up like the corners of a triangle. Most viewers see a solid white triangle sitting on top, complete with sharp edges and a brighter interior, even though no lines or contrast change exist anywhere on the page. Your visual system completes the shape it expects, edges and all.