The illusion is made of a two-dimensional figure . The visual system and the brain subconsciously interpret it as a projection of a three-dimensional object . An impossible object ( also known as an impossible figure or an undecidable figure ) is a type of optical illusion consisting of a two-dimensional figure which is instantly and subconsciously interpreted by the visual system as representing a projection of a three-dimensional object although it is not actually possible for such an object to exist ( at least not in the form interpreted by the visual system ) .