The reader or the audience knows something that the character ignores, so the character’s words and acts take on a meaning that he himself does not perceive.
In Hamlet
'The Mousetrap.' Marry, how? Tropically. [...] Your Majesty, and we that have free souls, it touches us not
The audience knows that “The Mousetrap” is a trap set by Hamlet, so the king’s question and the prince’s answer carry more weight for the audience than the king lets show.
Act III: The Mousetrap and the death of Polonius, Hamlet, to Claudius
That cannot be, since I am still possessed / Of those effects for which I did the murder: / My crown, mine own ambition, and my queen. / May one be pardoned and retain th' offense?
Act III: The Mousetrap and the death of Polonius, Claudius, alone
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