Van Manderpootz had forgotten his anger by the next time I dropped in for an evening. The robot still stood in the corner near the window, and I lost no time asking its purpose. "It's just a toy I had some of the students construct," he explained. "There's a screen of photoelectric cells behind the right eye, so connected that when a certain pattern is thrown on them, it activates the mechanism. The thing's plugged into the light-circuit, but it really ought to run on gasoline." "Why?" "Well, the pattern it's set for is the shape of an automobile. See here." He picked up a card from his desk, and cut in the outlines of a streamlined car like those of that year. "Since only one eye is used," he continued, "The thing can't tell the difference between a full-sized vehicle at a distance and this small outline nearby. It has no sense of perspective." He held the bit of cardboard before the eye of the mechanism. Instantly came its roar of "_A-a-gh-rasp!_" and it leaped forward a single pace, arms upraised. Van Manderpootz withdrew the card, and again the thing relapsed stolidly into its place. "What the devil!" I exclaimed. "What's it for?" "Does van Manderpootz ever do work without reason back of it? I use it as a demonstration in my seminar." "To demonstrate what?" "The power of reason," said van Manderpootz solemnly. "How? And why ought it to work on gasoline instead of electric power?" "One question at a time, Dixon. You have missed the grandeur of van Manderpootz's concept. See here, this creature, imperfect as it is, represents the predatory machine. It is the mechanical parallel of the tiger, lurking in its jungle to leap on living prey. _This_ monster's jungle is the city; its prey is the unwary machine that follows the trails called streets. Understand?" "No." "Well, picture this automaton, not as it is, but as van Manderpootz could make it if he wished. It lurks gigantic in the shadows of buildings; it creeps stealthily through dark alleys; it skulks on deserted streets, with its gasoline engine purring quietly. Then--an unsuspecting automobile flashes its image on the screen behind its eyes. It leaps. It seizes its prey, swinging it in steel arms to its steel jaws. Through the metal throat of its victim crash steel teeth; the blood of its prey--the gasoline, that is--is drained into its stomach, or its gas-tank. With renewed strength it flings away the husk and prowls on to seek other prey. It is the machine-carnivore, the tiger of mechanics." I suppose I stared dumbly. It occurred to me suddenly that the brain of the great van Manderpootz was cracking. "What the--?" I gasped. "That," he said blandly, "is but a concept. I have many another use for the toy. I can prove anything with it, anything I wish." "You can? Then prove something." "Name your proposition, Dixon." I hesitated, nonplussed.