Panes of transparent glass intersect and overlap. Starting anywhere, you can interpret what you see as part of a three dimensional object, but whose orientation is unclear. As your eyes continue along a path, you will find edges that force the panes to take a specific orientation. But if you try to extrapolate, you find contradictions: panes that looked horizontal now seem to be vertical, or vice versa. On a larger scale, it is impossible to perceive this scene as a definite physical object that can live in three dimensions.