“The door refused to open. It said, “Five cents, please.” He searched his pockets. No more coins; nothing. “I’ll pay you tomorrow,” he told the door. Again he tried the knob. Again it remained locked tight. “What I pay you,” he informed it, “is in the nature of a gratuity; I don’t have to pay you.” “I think otherwise,” the door said. “Look in the purchase contract you signed when you bought this conapt.” In his desk drawer he found the contract; since signing it he had found it necessary to refer to the document many times. Sure enough; payment to his door for opening and shutting constituted a mandatory fee. Not a tip. “You discover I’m right,” the door said. It sounded smug. From the drawer beside the sink Joe Chip got a stainless steel knife; with it he began systematically to unscrew the bolt assembly of his apt’s money-gulping door. “I’ll sue you,” the door said as the first screw fell out. Joe Chip said, “I’ve never been sued by a door. But I guess I can live through it.”

― Philip K. Dick, Ubik