While I have never read the book (because it is historically inaccurate - so don't get too sad, because it never could have happened), there are many words that would signal a flashback. Flashbacks are a time of reflection, so there are many past tense verbs used. You may also see things like, "Back in my day...", "As I think back...", "When I was a young boy...", "As I remember...".
