A man sat in the chair, motionless, silent. A weight dropped, crashed downward, then pounded aside at the last moment under the synchronized thump of a sudden force beam.

Only once—

And from her small camp chair in the observing booth in the balcony, Dr. Susan Calvin rose with a short gasp of pure horror.

Sixty-three robots sat quietly in their chairs, staring owlishly at the endangered man before them. Not one moved.

Dr. Calvin was angry, angry almost past endurance. Angry the worse for not daring to show it to the robots that, one by one, were entering the room and then leaving. She checked the list. Number twenty-eight was due in now—Thirty-five still lay ahead of her.

Number Twenty-eight entered, diffidently.

She forced herself into reasonable calm. “And who are you?”

The robot replied in a low, uncertain voice, “I have received no number of my own yet, ma’am. I’m an NS-2 robot, and I was Number Twenty-eight in line outside. I have a slip of paper here that I’m to give to you.”

“You haven’t been in here before this today?”

“No, ma’am.”

“Sit down. Right there. I want to ask you some questions, Number Twenty-eight. Were you in the Radiation Room of Building 2 about four hours ago?”

The robot had trouble answering. Then it came out hoarsely, like machinery needing oil, “Yes, ma’am.”

“There was a man who almost came to harm there, wasn’t there?”

“Yes, ma’am.”

“You did nothing, did you?”

“No, ma’am.”

“The man might have been hurt because of your inaction. Do you know that?”

“Yes, ma’am. I couldn’t help it, ma’am.” It is hard to picture a large expressionless metallic figure cringing, but it managed.

“I want you to tell me exactly why you did nothing to save him.”

“I want to explain, ma’am. I certainly don’t want to have you… have anyone… think that I could do a thing that might cause harm to a master. Oh, no, that would be a horrible… an inconceivable—”

“Please don’t get excited, boy. I’m not blaming you for anything. I only want to know what you were thinking at the time.”

“Ma’am, before it all happened you told us that one of the masters would be in danger of harm from that weight that keeps falling and that we would have to cross electric cables if we were to try to save him. Well, ma’am, that wouldn’t stop me. What is my destruction compared to the safety of a master? But… but it occurred to me that if I died on my way to him, I wouldn’t be able to save him anyway. The weight would crush him and then I would be dead for no purpose and perhaps some day some other master might come to harm who wouldn’t have, if I had only stayed alive. Do you understand me, ma’am?”

“You mean that it was merely a choice of the man dying, or of both the man and yourself dying. Is that right?”