Fulgour
The key phrase here in relation to the Convos card backsThe five regular polyhedra became known as the Platonic Solids. They are of great interest from a geometric standpoint. Remarkably, there are only five such shapes. The faces in each shape are regular polygons of the same size (tetrahedron - four triangles; cube - six squares; octahedron - eight triangles; icosahedron - twenty triangles; dodecahedron - twelve pentagons), and each can be inscribed in a sphere. It is not hard to understand that the simple beauty and perfect symmetry of these forms could have inspired Plato to attribute special significance to them. Copyright © 2007 American Chemical Society
seems to be "each can be inscribed in a sphere" as seen
in the central white O in the middle of Spalinger's design.
If you look at the O long enough, it begins to fluctuate...
this is I believe a natural optical illusion. Very mystical.