"As I said, they're the last. They survived only because they'd made a pilgrimage to a kind of underground shrine. The signals that killed the others didn't reach them through the layers of rock. Apparently the shrine had something to do with a planned revolt against the electronic law that governed them.
"It was an insidious law," Ernest went on, "with built-in enforcement. Any infraction could be punished instantly from central control in the palace. The infraction would trigger a shock wave, tuned to the individual frequency of the offender. The intensity of the wave was geared to the seriousness of the offense. Treason meant death from the strongest wave of all—the one that turned them to dust."
"Absolute rule," Doc said. "Pretty hopeless."
"Yes, in one way. But paradoxically they had an infinite amount of freedom of speech. You see that in their verses. No one was punished for what he said—only for what he did. I suppose it had to be that way, otherwise there'd have been wholesale slaughter."
"Which there was, at the end," Doc pointed out. "Who do you think exercised the control that killed all the others?"
"We did," Ernest said. "We killed them."