"The trailer herd," said Torcred. "Thousands on thousands of them, moving south with the sun that feeds them. The fall migration is farther west this year, and they are coming in greater numbers than any of our troop can remember." The girl said nothing. He added irritably, "You understand--there will be good hunting." She shocked him by laughing. "Is that all you think of?" she inquired mockingly. "Good hunting--a full stomach and a full fuel tank. You crawlers lead poor, empty lives." "We don't crawl," said Torcred shortly, eyes fixed on the speedometer that registered a hundred miles an hour. The bird-girl laughed again. "You know so little, you earthbound creatures," she taunted. "You've never known the joy of flight--to climb up and into the clear bright stratosphere, and see the Earth with all its secrets unroll below you.... _You_ creep from place to place and cower in your camps, but we range farther than you dream, and know the world and all its peoples that fly and swim and crawl and burrow. And we are the highest race of all." "Higher than the buzzards?" asked Torcred. She hesitated, then said defiantly, "Of course! Those evil things are huge and powerful, but we'll defeat them in the end, never doubt it. And then--we will have the rule of the sky, which is the rule of the Earth." She sounded very certain, and Torcred could think of no adequate counter-argument. He said brutally, "We? Who do you mean? _Your_ wings are clipped, bird!" Then unexpected remorse stung him as he saw how the girl shrank into herself, how the brief glow of enthusiasm left her face. She made no answer, and Torcred too fell sullenly silent. * * * * * In silence he closed the throttle and the hurtling terrapin slowed. Close ahead, now, the trailer herd was an amorphous black river in the gathering dusk. Earth and air shook to its thunder, the rumbling of countless wheels and engines and couplings and the strident bleating of thousands of horns as the vast herd jostled and protested. Closer and closer to the flank of the moving mass rolled the little terrapin, darting over the crests of the dunes and stealing along under their cover. The girl's eyes grew wide at the glimpses they had of that dark dangerous-looking stream; she seemed to flinch from its pounding clamor. Torcred smiled grimly as he brought the terrapin to a poised halt half-sheltered by a low swell. A scant hundred yards away the migrating trailers rolled obliviously past, one close behind the other, huge box-like monsters on wheels behind a tiny cab. Torcred knew their ways of old; the trailer sections housed women and children, who tended the apparatus that made food, fuel, and ammunition from sunlight and water and air and the minerals extracted from the sterile soil. The trailer-men were drivers and gunners; but the great machines were clumsy and ill-armed, finding safety against the fierce mechanical predators chiefly in their numbers.