Give a billion people phones and you might wire up a brain
Ned Block imagined the entire population of China, each person simulating one neuron by phone call, wired to replicate the exact firing pattern of a human brain in pain. Functionalism says anything playing the right causal role has real mental states, so this system should feel something. Block doubted a billion coordinated calls could ever add up to actual experience, no matter how perfectly they matched the pattern.