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The film crew was nearing the end of shooting, focusing on the intense conflict between Joker and Batman.
Seeing Martin smile broadly and laugh with others on set every day made Bale feel so irritable he wanted to kill someone.
Moreover, after shooting the hospital explosion scene, inspired by Nicholson, Martin added an impromptu element to his performance, making an explosive "bang" with his mouth when laughing crazily.
Nolan thought it was great and very fitting for Joker's reckless and maniacal demeanor, so he fully supported Martin.
But whenever Bale saw that mouth shape and heard that faint "bang" sound, he would subconsciously clench his legs together, and a nameless anger would stir in his heart.
Even sleeping at night, he would wake up from the ripping pain in his nightmares over and over again.
Bale's mental state deteriorated, and he had a full tank of anger that needed to be vented.
