Hafner nodded to himself. "Then we'll never be free from pests." He clasped and unclasped his hands. "Unless, of course, we rid the planet of all animal life." "Radioactive dust?" asked the biologist. "They have survived worse." The exec considered alternatives. "Maybe we should leave the planet and leave it to the animals." "Too late," said the biologist. "They'll be on Earth, too, and all the planets we've settled on." Hafner looked at him. The same pictures formed in his mind that Marin had thought of. Three ships had been sent to colonize Glade. One had remained with the colonists, survival insurance in case anything unforeseen happened. Two had gone back to Earth to carry the report that all was well and that more supplies were needed. They had also carried specimens from the planet. The cages those creatures were kept in were secure. But a smaller species could get out, must already be free, inhabiting, undetected, the cargo spaces of the ships. There was nothing they could do to intercept those ships. And once they reached Earth, would the biologists suspect? Not for a long time. First a new kind of rat would appear. A mutation could account for that. Without specific knowledge, there would be nothing to connect it with the specimens picked up from Glade. [Illustration] "We have to stay," said the biologist. "We have to study them and we can do it best here." He thought of the vast complex of buildings on Earth. There was too much invested to tear them down and make them verminproof. Billions of people could not be moved off the planet while the work was being done. They were committed to Glade not as a colony, but as a gigantic laboratory. They had gained one planet and lost the equivalent of ten, perhaps more when the destructive properties of the omnivores were finally assessed. A rasping animal cough interrupted the biologist's thoughts. Hafner jerked his head and glanced out the window. Lips tight, he grabbed a rifle off the wall and ran out. Marin followed him. * * * * * The exec headed toward the fields where the second fast crop was maturing. On top of a knoll, he stopped and knelt. He flipped the dial to _extreme charge_, aimed, and fired. It was high; he missed the animal in the field. A neat strip of smoking brown appeared in the green vegetation. He aimed more carefully and fired again. The charge screamed out of the muzzle. It struck the animal on the forepaw. The beast leaped high in the air and fell down, dead and broiled. They stood over the animal Hafner had killed. Except for the lack of markings, it was a good imitation of a tiger. The exec prodded it with his toe. "We chase the rats out of the warehouse and they go to the fields," he muttered. "We hunt them down in the fields with dogs and they breed tigers." "Easier than rats," said Marin. "We can shoot tigers." He bent down over the slain dog near which they had surprised the big cat.