The car refused to drive autonomously. It said, “$8.50, please.” He searched his pockets. No more coins; nothing. “I’ll pay you tomorrow,” he told the car. Again he tried the self-driving 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 car said. “Look in the purchase contract you signed when you bought this VW Bug.”

In his glove compartment he found the contract; since signing it he had found it necessary to refer to the document many times. Sure enough; payment to his car for taxiing him about while he listened to his morning HN podcast constituted a mandatory fee. Not a tip. “You discover I’m right,” the car said. It sounded smug.