“I don’t know,” said Thumper. “Uh, that is, I don’t know whether I need it or not. How do you know it works?”

Harry scoffed. “Man, everybody in the company knows it works. Time the robots come over the hill lookin‘ to kick butt, the purple cammy did the job. Ask the captain; ask Brandy; ask anybody-they’ll tell you. You want to be safe from robots, you gotta be wearin’ the purple.”

“I see,” said Thumper, his ears perking up. “But do we know that it protects against alien robots, Sergeant? Wouldn’t those have different laws?”

“What you mean, different laws?” asked Harry.

“Everybody knows robots can’t see purple-they just built that way.”

“I’m sorry, Sergeant, I must not have explained my point clearly,” said Thumper. “Let me try again. The brains of Alliance robots are all built with Asimov circuits that make them obey the Three Laws. Am I right?”

“Sure,” said Harry. “They can’t build ‘em no other way. And one of the things they build into those circuits is purple-blindness. I can show you that in writin’, Thumper, writin‘ straight from the gov’ment.”

“That’s very good, Sergeant,” said Thumper. “Of course I know the Three Laws-a robot mustn’t harm a sophont, or let a sophont come to harm if it can prevent it-we learned all that in kiddygarden. And the teachers wouldn’t tell us something if it wasn’t so. But what happens if we run into robots that weren’t made in the Alliance? Wouldn’t alien robots have different laws?”

“Alien robots? There ain’t no alien robots, on account of there ain’t no aliens,” said Harry, his voice getting louder. “Everybody’s part of the Alliance-all the so-phonts in the galaxy. So all the robots is the same.”

“But there are new sophonts discovered all the time,” said Thumper. “There are two races of them, both living right on this planet, that nobody knew about until the captain discovered them. What if the Zenobians had been building robots before we met them? Wouldn’t their laws be different? What about the Nanoids?”