Heath Ledger improvised when he started clapping inside his jail cell in a mocking and sardonic capacity as Gordon is promoted. The clapping was not scripted but Nolan immediately encouraged the crew to continue filming and the sequence was included in the film.
Also in the scene outside the hospital, just before it finally explodes, the explosives onset had stalled, so Heath improvised the scene and played around with the bomb remote.
and
Heath Ledger directed both homemade videos that the Joker sends to GCN himself. The first video involving the fake Batman was done under Nolan’s supervision. Nolan thought Ledger had done so well with that sequence, he felt there was no need for him to be there when it came time to film the scene where reporter Mike Engel reads the Joker’s statement. He put his trust in Ledger and let him do whatever he wanted, ultimately pleased with the result after he’d seen the outcome.
and
The Joker’s distinctive tongue flip grew out of Heath Ledger’s own habit of doing that.
and the part of the movie where the Joker walks in on the mob and says, “And I thought my jokes were bad.”? The words in the original script were actually, “And I thought I told bad jokes,” but apparently Heath changed it.
This is one of the reasons why I like this dude. He doesn’t merely act, he also contributes to the movie.
