Chalmers made the conundrum vivid by promoting the idea of a “philosophical zombie,” a complicated mechanism set up to behave exactly like a human being, with the same information processing in its brain, but with no consciousness. You stick a knife in such a zombie, and it screams and runs away. But it doesn’t actually feel pain. When a philosophical zombie crosses the street, it carefully checks that there is no traffic, but it doesn’t actually have any visual or auditory experience of the street.