A new film about Robin Williams begins with his appearance on Inside the Actors Studio with James Lipton. Lipton says: "How do you explain the mental reflexes that you deploy with such awesome speed? Are you thinking faster than the rest of us? What the hell is going on?" Williams first makes a goggle-eyed face, but then he falls over sideways, like an embarrassed kid, curling up and cackling. And then, of course, he does precisely the thing Lipton is asking about: a flurry of movements, voices, bits, fragments of thoughts flying by — fragments riffing on his own thinking.