I was riding a bus in Minneapolis and passed under a bridge. Someone had spray painted a row of triangles with a line from the tip to the base diagonally, at a slightly different angle on each one. The simple diagonal line transforemd the triangles into pyramids. It inspired me to create the P5 sketch below. In the first version of this sketch a vertical line simply moved from left to right, but then I realized it would look more realistic if I moved extended that line toward the viewer.