Early in the film, it isn’t hard to picture Arthur as a harmless mother’s boy, albeit a little nuts of course. “I’m not supposed to have a gun” is his hushed response when he is given a gun ‘for protection’ by his colleague, Randall. But destiny has other plans. 

It is the most important scene of the film, and the gun is the most important symbol of the film, representing this definitive turning point. It is also making a poignant point: Arthur is very strange and mentally ill, but the start of the film sees him as a nice man, one who takes care of his mother.

But the gun drastically changes his perspective of the world. Suddenly, this awfully cruel world, from Arthur’s deluded perspective, can now be altered. Violently. Having just been jumped by a bunch of kids, his self confidence needed a boost, and it seems this gun is just what the doctor ordered, given he can no longer get his medication.

This single scene also depicts the reality of gun availability and mental illness coinciding: arguably the exact reason for the despicable shootings in the US. The film could not be more relevant or timely. 

Back to the movie, the Gun clearly represents the beginning of his violent transformation, but it seems a part of Arthur never wanted to become such a violent monster. Arthur kills Randall in a fashion without a gun, as if he demonstrating that having a gun turned him into a violent man, even if he doesn’t have a gun in his hand. His obvious relief after the brutal murder of Randall suggests that it was an act of revenge, given Randall was responsible for the beginning of Arthur’s transformation. He gave him the Gun. Perhaps there was a part of Arthur, somewhere, that never agreed with his own actions.

After he learns he is to be on Murray’s show, he begins to practice how he will introduce himself on the show while watching an episode, most probably seeing himself in the studio as he did earlier in the film. His hallucinations are cleverly presented in a very different fashion this time around: from our perspective of the scene, the sound of the episode he is watching becomes crowd reaction to what Arthur is saying. The whole audience laughs at his joke, and he in turn reacts to the crowd. We see his first real smile before he delivers his punchline: putting his gun to his throat, he pulls the trigger, throwing his body back and goes limp.

Of course metaphorically, the gun was loaded. Arthur Fleck is dead, and the Joker is  born.

Meanwhile, another gun creates true mayhem on the subway: as a cop is chasing the Joker, he accidentally shoots and kills a man – instantly he is surrounded by the other passengers, who jump on him. The Joker is free, and after getting off the train, he does another quick dance, and happily skips away, throwing away the clown mask he used to blend with crowd. The camera closes in on the mask, suggesting that Joker is now able to throw away his metaphorical mask, free to act in the way he wants.

This soon becomes very apparent when he is introduced on to the stage of his favourite show. He suddenly looks confident, and performs a quick dance for the audience, and then surprises the female guest with a long kiss before sitting down. As Murray says, it is quite the introduction

The Joker’s sense of humour is presented incredibly accurately while he is on the show. His ‘knock knock’ joke has the crowd displeased, and then the female guest tells him that the joke isn’t funny. His rant about comedy being subjective couldn’t be more accurate. The woman telling him that his joke can’t be funny on a show like Murray’s family-friendly entertainment is reminiscent of the Letterman show when he decided to cut the comedy routine of Bill Hicks.

While it is probably unintentional, this is an interesting look at what comedy is. Confessing that he shot three people who were ‘awful’, he is proud, telling Murray that what he did was a funny, a joke that aligns perfectly with humour of the Joker of other films/games. Murray tells him that the shooting is what caused the riots in Gotham, eliciting a smile from the Joker as he raises up his hand, taking responsibility and chuckling at his own joked. This again is amazing in its perfect connection to the Joker’s sense of humour. This is a guy whose idea of a joke is to blow up a building, or to shoot his former idol in the head.