Joaquin Phoenix based his laugh on "videos of people suffering from pathological laughter." He also sought to portray a character with which audiences could not identify. Pathological laughter is a real-life disorder which causes the patient to suffer from uncontrollable laughter attacks in response to tense or stressful situations. Although the disorder isn't usual, these attacks can stop the normal flux of oxygen to the brain or lungs, causing hypoxia or even asphyxia in the patient.
The film is the first R-rated movie in history to make $1 billion worldwide.
In a recent interview with SFX magazine, Joaquin Phoenix acknowledged that while the violence in "Joker" is "a little more visceral and raw" than films such as the Avengers series, he "didn't have any hesitation about it." "You always want it to feel real, and you want the little violence that we have to have an impact," he said. "What happens in a lot of movies is that you get numb to it, you're killing 40,000 people, you don't feel it. While being a fictional story in a fictional world, you always want it to feel real. Everything that happens in this movie as far as violence goes, you feel it."
Joaquin Phoenix said about the 52 lb weight loss: "Once you reach the target weight, everything changes. Like so much of what's difficult is waking up every day and being obsessed over like 0.3 pounds. Right? And you really develop like a disorder. I mean, it's wild. But I think the interesting thing for me is what I had expected and anticipated with the weight loss was these feelings of dissatisfaction, hunger, a certain kind of vulnerability and a weakness. But what I didn't anticipate was this feeling of kind of fluidity that I felt physically. I felt like I could move my body in ways that I hadn't been able to before. And I think that really lent itself to some of the physical movement that started to emerge as an important part of the character."
Todd Phillips: [popular songs from whatever era the film takes place in are played throughout the film] The film has several songs from the late 1970s and early 1980s being played. Similarly, in some of Phillips' films, Una notte da leoni (2009) and Una notte da leoni 2 (2011), popular songs from the late 2000s to early 2010s are played.