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The Dark Knight (2008)
In the hospital scene, where the Joker staggered out of Gotham General with the hospital exploding around him, the Joker twiddled with the detonator when the explosions had stopped before suddenly continuing. Heath Ledger didn't break character (rumours about it being a mistake by the effects team surfaced, which eventually turned out to be intentional), nor did he even turn to watch the explosion even when he got on the bus. It all built up to one of the most memorable scenes in the movie, with everything executed perfectly.