I have become fascinated with the intersection of shapes. The edge that is formed when two surfaces intersect. These intersections are often seen in the mind of the mathematician but for others who see the world as flat images on the retina of eyeballs the volumetrics are difficult to imagine. This is a sort of puzzle film... the beginning of a series of films and the honing of a technique to make the invisible visible.
The first half is the geometry surface rendered. The second half is the intersections of the geometry with a plane and any geometrical boundary intersection. Here I am making this in Maya, I turn off all the surfaces from the render pipeline. Assign on "Toon Outlines" and turn off everything but the toon curves made by the intersections.