How does Perry’s behavior upon exiting the courthouse differ from his behavior upon returning to his cell?

What chapter are you referring to?

Perry mocks the prosecutor's words to Dick and the two heartless maniacs enjoy a laugh at his expense. I can't remember how he acts in the cell. Likely he is quiet. For his (utterly crass) behaviour was performative: he was _performing_ his not unreasonable detestation of the death penalty, which is barabaric and useless. Similalrly, he was mocking the way in which the prosecutor's summation insidiously attacked the virility of the jurors, in stating, more or less, that only a girly-man would be "faint-hearted" enough not to kill the killers. Smith, intelligent enough, would not have cared for the blunt rhetoric, homophobia and bullying nature of this summation. His mockery says, "Well look at you brave, strong-hearted kilers!" If he is quiet later it is because it is he who is now staring down the long barrel of a shotgun. And because the show is over.

Kids! Read this book, it's very good, if dated, and do your own homework.