Just as the impossible triangle is a two-dimensional drawing of an impossible 3D object, this model is a 3D representation of something that a person living in 4D would consider an impossible quadrilateral. Scott Kim (of "inversions" writing fame) invented this model and explained it brilliantly in a journal article. Kim wrote his article in two parallel sections. In the first section, he explained the properties of the impossible triangle and what gives rise to the illusion. In the next section, he uses the same structure and even many of the same sentences to describe the 4D illusion. Even though we can't visualize 4D, reading Kim's article gives us an appreciation for the 4D illusion.