The man with thick glasses waved an arm. The Minister for Health went hastily out. Dr. Lett made a mirthless sound. "He would not make a medical man! Here is a para in this aseptic room. He is an unusually good specimen for study. He was my assistant and I knew him when he was sane. Now I know him as a para. I will show you his delusion." He went to a small culture oven and opened the door. He busied himself with something inside. Over his shoulder he said with unction: "The first settlers here had much trouble establishing a human-use ecology on this world. The native plants and animals were useless. They had to be replaced with things compatible with humans. Then there was more trouble. There were no useful scavengers--and scavengers are essential! The rat is usually dependable, but rats do not thrive on Tallien. Vultures--no. Of course not. Carrion beetles ... Scarabeus beetles ... The flies that produce maggots to do such good work in refuse disposal.... None thrive on Tallien Three! And scavengers are usually specialists, too. But the colony could not continue without scavengers! So our ancestors searched on other worlds, and presently they found a creature which would multiply enormously and with a fine versatility upon the wastes of our human cities. True, it smelled like an ancient Earth-animal called skunk--butyl mercaptan. It was not pretty--to most eyes it is revolting. But it was a scavenger and there was no waste product it would not devour." Dr. Lett turned from the culture oven. He had a plastic container in his hand. A faint, disgusting odor spread from it. "You ask what the delusions of para may be?" he grinned derisively. He held out the container. "It is the delusion that this scavenger, this eater of unclean things, this unspeakable bit of slimy, squirming flesh--paras have the delusion that it is the most delectable of foodstuffs!" He thrust the plastic container under Calhoun's nose. Calhoun did not draw in his breath while it remained there. Dr. Lett said in mocking admiration: "Ah! You have the strong stomach a medical man should have! The delusion of the para is that these squirming, writhing objects are delightful! Paras develop an irresistible craving for them! It is as if men on an Earth-like world develop an uncontrollable hunger for vultures and rats and--even less tolerable things. These scavengers--paras eat them! So normal men would rather die than become paras!" * * * * * [Illustration] Calhoun gagged in purely instinctive revulsion. The things in the plastic container were gray and small. Had they been still, they might have been no worse to look at than raw oysters in a cocktail. But they squirmed. They writhed. "I will show you," said Dr. Lett amiably.