An impossible object is a manipulative puzzle
in which the aim is to deduce how the object was made. The term is also used to refer to a type of optical illusion
in which a photo of a three-dimensional figure is interpreted by the visual system as an object that defies the laws of physics. An example is the Necker cube shown on this page. Look carefully at it. Do you think it's possible to build such a thing?
Also Known As: impossible figure, undecidable figure