Cyclic Cellular Automaton

A model demonstrating self-organizing spirals and waves out of pure noise.
There are 6 states forming a loop (0 → 1 → 2 → 3 → 4 → 5 → 0). A cell in state S advances to state S+1 if and only if it has at least one neighboring cell already in state S+1 (it gets "eaten" by the next state in the food chain).
Starting from complete randomness, small "seeds" of sequential states emerge and eventually dominate the entire grid with beautiful rotating spiral waves, reminiscent of excitable media like heart muscle tissue.