"Shut up!" said Powell, savagely, "I know you know it, but I’m just describing the hell of it. Those six subsidiaries are part of DV-5 like your fingers are part of you and it gives them their orders neither by voice nor radio, but directly through positronic fields. Now—there isn’t a roboticist back at United States Robots that knows what a positronic field is or how it works. And neither do I. Neither do you."