In the space between a bird and a fish, there exists a shape that is both and neither. M.C. Escher found it. He called it "filling the plane."
The Paradox
Each tile is complete. Each tile is incomplete. The bird exists only because the fish gives it form. The fish swims only in the spaces the bird does not fly.
The Harmony
Nature tessellates in honeycombs and scales. Mathematics tessellates in triangles and hexagons. Art tessellates in metamorphosis and wonder.
Look closely at any edge. Where does one end and another begin? The answer is: everywhere and nowhere.