They are the same size ... feel free to measure them!
The Kanizsa triangle is an optical illusion first described by the Italian psychologist Gaetano Kanizsa in 1955. In the image to the right, a white equilateral triangle is perceived, but in fact none is drawn.
The Necker cube is an ambiguous line drawing. It is a wire-frame drawing of a cube in isometric perspective, which means that parallel edges of the cube are drawn as parallel lines in the picture. When two lines cross, the picture does not show which is in front and which is behind. This makes the picture ambiguous; it can be interpreted two different ways. When a person stares at the picture, it will often seem to flip back and forth between the two valid interpretations (so-called multi stable perception) .
Do you see anything funny, strange, or wrong on the face of this clock?
Compare the numeral for the 4. Roll your mouse over the clock image to see the difference.
Originally all clocks had it as IIII, only to be changed later.