The iconic scene where the jokingly mocks commissioner Gordon by clapping was not part of the script. Ledger improvised the sarcastic applause and Nolan decided to continue filming.
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The highly visible tick where Ledger’s Joker keeps licking his lips was an action improvised by Ledger. He kept licking his lips to keep his mouth moist which he said helped him to speak in the Joker’s voice and keep the performance consistent.
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Heath Ledger was reported to always be in a dark frame of mind on set to stay in character. But what impressed everyone was the fact that he could just turn off the mood and turn it on when he wished.
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Ledger insisted on that every scene should be life like so when the Batman interrogates the Joker, Bale revealed that Ledger told him to beat him as hard as he could for the scene to seem authentic.
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