I can’t help but think about Backwards and Forwards with this bit. Because this is the line that really makes his case that Hamlet is not saying this speech for his own benefit. Because, the fact is, Hamlet has direct experience of a traveller returning from death. His father, who he saw interred a month prior, has shown up quite vividly before him. He’s had all kinds of descriptions of the “undiscovered country.” He’s heard about the rending flames, the horrors, the sin-burning, etc. So it is hard to see this bit as a real inquiring thought on Hamlet’s part. It starts to seem like poetic embroidery on a theme he is exploring for the benefit of his audience. It’s a beautiful poetic embroidery or maybe even the sort of embroidery anyone creating a fiction will do. When lying, for example, we usually keep talking to help make our case.