She mumbled something impatiently as Kallner half-rose to greet her, and went on, “We’ll have to try something else quickly. I don’t like what’s happening.”

Bogert exchanged a resigned glance with the general. “Is anything wrong?”

“You mean specifically? No. But I don’t like to have Nestor 10 continue to elude us. It’s bad. It must be gratifying his swollen sense of superiority. I’m afraid that his motivation is no longer simply one of following orders. I think it’s becoming more a matter of sheer neurotic necessity to outthink humans. That’s a dangerously unhealthy situation. Peter, have you done what I asked? Have you worked out the instability factors of the modified NS-2 along the lines I want?”

“It’s in progress,” said the mathematician, without interest.

She stared at him angrily for a moment, then turned to Kallner. “Nestor 10 is decidedly aware of what we’re doing, general. He had no reason to jump for the bait in this experiment, especially after the first time, when he must have seen that there was no real danger to our subject. The others couldn’t help it; but he was deliberately falsifying a reaction.”

“What do you think we ought to do now, then, Dr. Calvin?”

“Make it impossible for him to fake an action the next time. We will repeat the experiment, but with an addition. High-tension cables, capable of electrocuting the Nestor models, will be placed between subject and robot—enough of them to avoid the possibility of jumping over—and the robot will be made perfectly aware in advance that touching the cables will mean death.”

“Hold on,” spat out Bogert with sudden viciousness. “I rule that out. We are not electrocuting two million dollars worth of robots to locate Nestor 10. There are other ways.”

“You’re certain? You’ve found none. In any case, it’s not a question of electrocution. We can arrange a relay which will break the current at the instant of application of weight. If the robot should place his weight on it, he won’t die. But he won’t know that, you see.”

The general’s eyes gleamed into hope. “Will that work?”

“It should. Under those conditions, Nestor 10 would have to remain in his seat. He could be ordered to touch the cables and die, for the Second Law of obedience is superior to the Third Law of self-preservation. But he won’t be ordered to; he will merely be left to his own devices, as will all the robots. In the case of the normal robots, the First Law of human safety will drive them to their death even without orders. But not our Nestor 10. Without the entire First Law, and without having received any orders on the matter, the Third Law, self-preservation, will be the highest operating, and he will have no choice but to remain in his seat. It would be a forced action.”

“Will it be done tonight, then?”

“Tonight,” said the psychologist, “if the cables can be laid in time. I’ll tell the robots now what they’re to be up against.”