Christopher Nolan’s The Dark Knight introduced the Joker, played by Heath Ledger, who gave a unique performance of the Clown Prince of Crime and gave the character a unique tic: licking his lips constantly, and here’s why. Although Batman is one of the most popular and beloved comic book characters, he hasn’t always had good luck on the big screen. Following the success of Tim Burton’s Batman and Batman Returns, the Caped Crusader went through a rough patch with Joel Schumacher’s Batman Forever and Batman & Robin, but Batman, Gotham City, and its most notable residents were given another chance on the big screen in the 2000s with Christopher Nolan’s Dark Knight trilogy.

First was Batman Begins in 2005, which introduced the audience to Christian Bale as Bruce Wayne, as well as to Liam Neeson as Ra’s al Ghul and Cillian Murphy as Jonathan Crane/Scarecrow. The success of Batman Begins made way for the next two installments, The Dark Knight and The Dark Knight Rises, with the former standing out. The Dark Knight saw Batman go against the Joker, though a different version of the iconic villain from what had been previously seen in films. The Dark Knight was a critical and commercial success and is considered one of the best superhero movies ever made, with Ledger’s portrayal of the Joker often pointed out as the movie’s strength. Ledger brought some unique traits and mannerisms to the character, including a tic in which he constantly licked his lips.

Related: The Dark Knight: WB's Joker Origin Plan Would've Ruined The Movie

The Joker made his big-screen debut in the 1966 movie Batman, based on the TV series starring Adam West and Burt Ward, and was played by César Romero. Then came Jack Nicholson’s Jack Napier in Tim Burton’s Batman, considered one of the most loyal interpretations of the character as he captured the essence of the comic book villain quite well. Nolan’s version of the Clown Prince of Crime is a unique version, as he had to fit the style and tone of the movie, thus had to get rid of the character’s comic book-y elements, and instead brought a darker, more psychopath Joker. Ledger’s version was also less polished in terms of physical appearance, and constantly licked his lips, which became his trademark mannerism, and it wasn’t actually something Ledger planned, instead being something he did out of impulse and necessity.

 Joker licking lips in The Dark Knight

Although the Joker’s clown makeup was simpler and messier than those of Nicholson and Romero’s versions, Ledger’s version required the use of prosthetics to make his signature facial scars. In the documentary I Am Heath Ledger (via Digital Spy) it’s revealed that, in order to keep the prosthetics in their place as they got loose when he spoke, Ledger had to lick his makeup to keep it in place, and it ended up becoming part of the Joker’s manic personality, as well as his most memorable mannerism. This tic also made the character look menacing and “hungry” for chaos, more so as he tended to stare directly into whoever he was talking to while licking his lips.

When The Dark Knight was released, many fans thought it was an odd choice to have the Joker licking his lips every time he spoke, but it’s proof of the level of Ledger’s craft, as he was able to effortlessly make something practical part of the character. Even though there have already been other versions of the Joker since The Dark Knight came out (Jared Leto’s in the DCEU and Joaquin Phoenix’s in Joker), Heath Ledger’s version stands as one of the best and darkest adaptations of the character, made unforgettable thanks to the personal touch Ledger gave to the character and the addition of mannerisms like constantly licking his lips.

Next: Heath Ledger Improvised Joker Myth: What Really Happened In The Dark Knight