I hadn't really thought of Zombies in the context of CAS, but it does sort of work, at least to a point. I have seldom seen them form anything like a stable system, but I suppose you could say that the enormous piles of Zombies that stayed constantly outside the prison for all those weeks might arguably represent one. 

Your recommendation is excellent. Anyone who wants to understand systems, chaos and complexity at a much deeper level should visit complexity explorer. It's a free resource, with outstanding courses taught by true thought leaders in the CAS world.