"It was," Sagan said. "And as it happens, by the very sort of defense system you specialize in. We didn't know that at the time, of course, but we know it now."

"How did you find the base if it was shielded?" Cainen asked. "I am curious, in a professional sense."

"We dropped rocks," Sagan said.

"Excuse me?" Cainen asked.

"Rocks," Sagan said. "A month ago we salted the planet with several dozen seismic sensors, which were programmed to look for seismic signatures that suggested intelligently designed underground structures. Speaking from experience, secret bases are easier to shield when they're underground. We relied on the planet's natural seismic activity to narrow down areas to investigate. Then we dropped rocks in areas of interest. And then today we dropped several right before our attack, to get an exact sonic image of the base. Rocks are good because they look like naturally occurring meteors. They don't scare anyone. And no one shields against seismic imaging. Most races are too busy shielding against optical and high-energy electromagnetic scans to consider sound waves much of a danger. It's the fallacy of high technology; it ignores the efficiency of lower orders of technology. Like dropping rocks."

"Leave it to humans to bang rocks together," Cainen said.

Sagan shrugged. "We don't mind when the other guy brings a gun to a knife fight," she said. "It just makes it easier for us to cut out his heart. Or whatever it is that he uses to pump blood. Your overconfidence works for us. As you can see because you are here. But what we really want to know, Administrator, is why you are here. Eneshans and Rraey working together is puzzling enough, but Eneshans and Rraey and Obin? That's not just puzzling. That's interesting."

"I don't know anything about who owns this planet," Cainen said.

"And what's even more interesting is you, Administrator Cainen," Sagan said, ignoring Cainen's comment. "While you were sleeping we did a gene scan on you to tell us who you are, then we accessed ship's records to learn a little of your history. We know one of your primary areas of xenobiological interest is humans. You're probably the Rraey's leading authority on human genetics. And we know you've also got a particular interest in how human brains work."