Tragically famous actor Heath Ledger, who played the role of the cult Joker, get into character so much that he asked Christian Bale who played Batman not to imitate the blows but to beat him for real in the scene of interrogation in the cell. Ledger rushed to the walls with such a great force, that they were left with cracks.
This became known thanks to a new book by Joseph McCabe, who interviewed Bale, Ledger and film director Christopher Nolan back in 2007-2008. Bale and Nolan then told how much they were amazed at how Ledger got used to his role.
The role of the Joker is almost the best in the career of Heath Ledger - he has so convincingly get into the role of the crazy villain that even now the fans of the superhero universe do not see him as a worthy replacement.
According to most fans of the talent of the late actor, no one but Ledger himself could have played the Joker so effectively.
By the way, here
is a scene from the movie.