Why Joaquin Phoenix Was Sick Every Day Filming Joker 2

Performing in a major motion picture could give anyone butterflies, but Joaquin Phoenix found himself feeling sick to his stomach every day on the set of "Joker: Folie à Deux." Why? Because he had to keep up with Oscar-winning composer and actress Lady Gaga — at least, that's what happened, according to director Todd Phillips. That's a whole lot of anxiety to deal with, but it looks like he and Lady Gaga managed to make it through the storm thanks to their ability to support one another.

Phillips said that the duo's mutual admiration society helped them both get through the shoot with grace, which ultimately helped them turn in complete performances. "The truth is, they gave each other pointers," he told Entertainment Weekly. "He'd give her pointers about acting; she's been in movies, but he's Joaquin Phoenix. She gave him tips about music because she's Lady Gaga. It's what movies should be: a giant collaboration."

While Phoenix ultimately got past his nausea, the film's musical production numbers definitely required some careful forethought. Phillips had a master plan for the movie's soundtrack, though — and it has a special meaning for Arthur Fleck (Phoenix) and his apparent soulmate, the film's darker take on Harley Quinn, Lee Quinzel (Gaga), as they traverse the warm emotional interior of their rather icy world.

Show tunes, big band numbers, and other catchy, horn-driven pieces make up the soundtrack for "Joker: Folie à Deux," including takes on songs originally sung by Frank Sinatra, Judy Garland, the Carpenters, and more. There is, of course, a reason behind Todd Phillips' musical choices for the film. The director said that the song selection represents Arthur's newfound love for Lee, and the music the twosome "performs" are mainly songs Arthur's mother used to play when he was younger. Because of this, "It's not weird that he knows the lyrics to something like, 'For Once in My Life,'" Phillips explained to EW, adding that he has no idea if the original singers had truly experienced the emotions they sang about. But when Arthur sings them as a man who genuinely never has been wanted or needed by another human being until now, the lyrics reflect exactly what he's feeling.

"There's a light, a beauty, and a romance inside of him ... [Y]es, he's out of step with the world. However, there's a romance inside of him, and there's music inside of him," Phillips explained. "What happens when a guy who hears music inside his head finds love for the first time in his life? Maybe the music that he hears inside his head starts coming out. Why wouldn't that music come out when he meets somebody who gives him the time of day? His biggest issue in the first movie, outside of childhood trauma, was a severe lack of love." Lee, Phillips said, completes Arthur's need for true affection, while Arthur completes Lee's need for a man of action. But where do these big-time moments happen? Well, it's not in the reality the characters really exist in.

"The Joker" was more or less a reality-based movie, with Arthur's flights of emotional fancy mainly caged within the gutters through which he pranced like the clown prince he sees himself as. It turns out that the musical numbers in "Joker: Folie à Deux," however, take place solely within the character's delusions, which explains, among other things, how and why Arthur and Lee have access to the "Tonight Show" set. This is a fitting approach to the film's use of music if you know the meaning behind the French phrase, "folie à deux."

But is the movie a full-on musical? Todd Phillips initially refused to classify his sequel this way, mostly because of his feelings about how the genre ought to make you feel. But as the release day nears, the director seems to be having second thoughts about that. "I got a little heat for saying it's not really a musical," he told Entertainment Weekly. "I wasn't saying that because I'm afraid of the term, 'musical.' I love musicals, and the movie definitely has music in it. It might even be a musical. To clarify, most of the times I've ever seen a musical, I walk out feeling better than I did when I walked in. On this movie, I'm not sure it's the same thing. I wouldn't want to be misleading and say you're going to be whistling the songs from this movie on the way to your car after you see it."

While the sequel is getting mixed reviews, DC fans will find out whether seeing Arthur feeling bad and singing duets with his new love — if only in his mind — can make them feel good when "Joker: Folie à Deux" hits theaters on October 4.