In preparation for his role as The Joker, Heath Ledger hid away in a motel room for about six weeks. During this extended stay of seclusion, Ledger delved deep into the psychology of the character. He devoted himself to developing The Joker’s every tic, namely the voice and that sadistic-sounding laugh.
Joker by Stephane Roux
From the Batman: Arkham Origins art book
This scene takes on a whole new meaning once you see what Bruce Timm drew them doing with a whoopee cushion.
The Killing Joke (1988)
Art by Brian Bolland
Story by Alan Moore