What is the dramatic irony in the scene between Creon and the sentry who brings news of Polyneices's burial in "Antigone"?

Dramatic irony is a situation in which a play's audience has information that the characters on the stage do not have. In the case of the messenger's announcing to Creon that his edict has been broken and that someone has buried Polyneices, the audience already knows who the culprit is. We know that Antigone is determined to give her brother a proper burial, regardless of Creon's law that whoever does so will be stoned to death. The audience will begin to wonder whether Creon will carry through with his threat when he learns that his own niece is the first person to disobey him.