 Before his departure, Peter recalls a line from a film. Why does it come to mind for him?
I do not think it was what Peter called an emotion; and yet it had nothing to do with logic, either. I did not even wish that Peter were not dead, for reason had told me that he had to die. He could see, too, the level on level of laboratories and storerooms that filled its interlocking segments; the meteor deflectors, the air renewal system, the mighty engines at the stern—all the children of his brain. The order was made public early this morning by R. Stein, Secretary of the Council, who said in part: "The reason for this ... order must be apparent to all civilized peoples. "The peoples of the world, then, know what they are, and know that we face the most momentous struggle in our history. They have treated us precisely as we, in less enlightened days, might have treated a newly-discovered race of lower animals. They have examined us, dissected us, driven us mad, killed us with no discernable provocation; and this is more intolerable than any normal invasion. Peter sank back in his chair, the full shock of it striking him for the first time. " Peter took it in fifteen seconds, running, and stumbled to a halt in front of the door marked "Radiation." She had set her door mechanism to "Etaoin Shrdlu," principally because he hated double-talk. It was a street scene in the Science City of Manhattan, flooded by the warm spring sunshine.
 He recognizes that he will be a changed, mutated man when he returns. He literally will come back "not as a boy."
 He recognizes that he will be a changed, mutated man when he returns. He literally will come back "not as a boy."  He's trying to convince himself that he and humanity will be able to come back, with the emphasis on "We'll come back."  The situation is grave. Like men who go off to war, the journey will change them. He won't be coming home as the same "boy."  He's not sure he'll be coming back, and the song is bittersweet for him.