The black comedy Frank centers around an exceedingly eccentric musician named Frank (Michael Fassbender) and his struggle to record a debut album (and masterpiece) with his just-as-weird band, Soronprfbs. The film follows keyboardist Jon (Domhnall Gleeson) as he becomes the newest member to join the group and get sucked into their strange, reclusive world.

The cast and filmmakers spoke about the challenges of building a fictional band while at a press conference for the film in New York City.

"I think the really hard task for these guys was to [write] music that was arty but not pretentious, and had a real truth to it that wasn't commercial but wasn't awful," said the film's star, Michael Fassbender. "It really was a huge undertaking for [the filmmakers], but I think they did a great job."

The results are mostly noisy, experimental jams, but believable enough as eccentric art rock. In the movie, "Coca Cola, Lipstick, Ringo, Dance All Night" is the title of the closest thing Frank's written to a pop song.

"It's never specified what mental illness Frank has," said screenwriter Jon Ronson. "But at that moment I was thinking, if someone with manic depression tried to write a Katy Perry song, how would it come out? And that [song] was 'Coca Cola, Lipstick, Ringo.'"

While promoting Frank, the film's cast stopped by The Colbert Report to perform another song, a ballad named "I Love You All," in character as the band Soronprfbs.

Like in their lone television performance, all of the music heard in Frank was actually played by the film's cast.

"All of us were pretty musical people," said Fassbender. "I've always liked music and it's always been in and around my life, so it was nice to fulfill a fantasy and play in a band."

"I think there really is a difference between being musical enough, and acting like you're excellent at it," said Maggie Gyllenhaal, whose character plays Theremin for Soronprfbs in the film. "I went to see Nick Cave play in Prospect Park the other day... they were so awesome. And we were acting like we were awesome."

The film was loosely inspired the character Frank Sidebottom, who was created by British musician and comedian Chris Sievey. Screenwriter Jon Ronson—who at one point had been a member of Sidebottom’s band—says only the film's first few scenes, where Domhall Gleeson's character joins the group, are true to life, while the rest of Frank’s story was totally fictionalized. The script changed quite a bit as it was developed with director Lenny Abrahamson; Maggie Gyllenhaal's character, Clara, appears to have undergone the heaviest transformation.

"Clara's part in the earliest version of the script was called Klaus," said Abrahamson. "[He] was a German, Kraut Rock, hardcore, uncompromising Klaus Kinski-type character."

"Frank was Wener Herzog, and Clara was Klaus Kinski," Ronson elaborated.

"Maggie brought this other dimension of a longing that she couldn't fulfill for a relationship with Frank," Abrahamson continued. "So that's what her journey became in the film."

Frank's hardest-to-miss element, of course, is the mask. Fassbender's performance takes place almost entirely underneath an oversized, papier-mache mask, which fit over the actor's head like a helmet. Abrahamson pointed out that masks have been used in drama for millennia, and that they better allow the audience to project their own feelings upon a character. Both he and Fassbender admired the mysterious quality it lent Frank, as the other characters in the movie could never read his facial expressions (or tell when he was even listening to them.)

"I found it really liberating," said Fassbender. "As soon as I put the head on it gave me an element of mischief. It gives it sort of an anarchic quality."

While it brought a level of enigma to Fassbender's character, the mask came with all of the downsides you'd imagine are part of wearing a large, heavy head for long periods of time (and under film lighting.)

"It was hot and sweaty in there, and sometimes you can't breathe as easily as you should," Fassbender explained. "It was like a beard that had gotten out of control. There were little crumbs in there. It was pretty gross."