"Bloody fools. They raise herbs and mola. If they didn't come, Venus would be uninhabited except by natives in a few years. The North-Fever ... You'd better watch out for that, by the way. If you start feeling rocky, see a doctor. Not that it'll help. But you can be put under restraint till the fever passes."
Vanning looked up. "I've heard of that. Just what—"
"Nobody knows," Goodenow said, shrugging hopelessly. "A virus. A filterable virus, presumably. Scientists have been working on it ever since Venus was colonized. It hits the natives, too. Some get it, some don't. It works the same way with Earthmen. You feel like you're cracking up—and then, suddenly—you go North. Into the swamp. You never come back. That's the end of you."
"Funny!"
"Sure it is. But—ever heard of the lemmings? Little animals that used to make mass pilgrimages, millions of them. They'd head west till they reached the ocean, and then keep going. Nobody knew the cause of that, either."
"What lies north?"
"Swamp, I suppose. How should I know? We've got no facilities for finding out. We can't fly, and expeditions say there's nothing there but the usual Venusian hell. I wish—"
"Oh-oh!" Vanning sat up, peering into the projector. "Wait a minute, Goodenow. I think—"
"Callahan? No!"