In a movie filled with musical mash-ups and comedic one-liners, one thing stands out about Pitch Perfect: the improvisational abilities of Australian-born actress Rebel Wilson, who plays Fat Amy, a girl with a wicked voice and a quick wit.

While speaking recently with Spinoff Online and other reporters, Wilson praised Kay Cannon’s script for the Universal Pictures release, which she viewed as a starting part for the character’s unfiltered observations. From there, Wilson added her own quips until director Jason Moore told her to stop.

One of Wilson's on-set inspirations, the so-called Mermaid Dance that appears near the beginning, added some expense to the production. "They didn't know I was going to go on the ground and start dancing, so in the original shot, they had tape marks all over the concrete," she recalled, referring to the tape used to show actors where to stand during scenes. "Jason wanted to use it in the movie, but there was all this tape so they had to digital-effect the tape out of the shot. I think it cost them thousands and thousands of dollars just to use that joke."

While she would enjoy seeing the Mermaid Dance catching on, she noted it may not be the best dance for clubbing. "The problem is [the] club floors,” she said. “They're very disgusting, and so imagine if it became a club craze with all these people dancing on the floors with all this slime!"

Pitch Perfect follows Beca (played by Anna Kendrick), who, despite her dream of becoming a radio DJ, is forced to go to college. There, she joins an all-girls a capella group called The Bellas, which is determined to defeat the reigning Treble Makers in an international competition.

Like Fat Amy, Wilson took part in an a capella group at school. "It was called 'Twelve Voices' because there were 12 girls in it. Y'know, how original," she recalled. "I went to a Christian school, so we'd sing church songs at people's weddings and funerals and stuff. We had to wear these peasant blouses and these disgusting velvet long skirts." The routines also featured stiff choreography that Wilson said resembled the sort her group performs in the early part of the film. Another reflection of Twelve Voices in the film: She was an alto, just like Fat Amy.

Despite that early experience in performing, Wilson didn’t expect to do it professionally; her plans included law school. "When I finished high school, I was a youth ambassador for Australia and I was based in southern Africa for a year and spread good will across the African continent," she said. "As part of my job, I got malaria really badly and was put in intensive care." During her recovery, a "cocktail they give you to fix you and make sure you don't die" gave her a hallucination of stardom.

"In this hallucination, I was at the Oscars and I won and I was a really good actress and it was so real that when I came out of hospital, I was saying to people that I'm going to become an actress," she continued. Those around her suggested she should stay on her chosen path and finish up law school, but Wilson decided to stick with the hallucination and returned to Australia a month later ready to start theater school. "It took a while because girls who look like me or are from the poorer area where I'm from in Australia, you just don't think that would happen," she said.

At first, she wrote and performed her own musicals, which quickly got her on Australian TV and seen by American agents. "I'd written a musical television series in Australia called Bogan Pride," she said. "There was a clip where I was in a swimming costume, like a bathing suit, and I had pubic hair and they showed it to William Morris Endeavor, my agency here, and they said, 'Yup, she might be the next Dame Judi Dench.’”

Although her hallucination led her to move to the United States, Wilson misses Australia and only recently returned from a trip home. "It's a very long way to come,” she said. “All my family's there, so I try go back when I can. But the movies are just keeping me so busy, which is great."

In the case of Pitch Perfect, the movies also present plenty of unexpected challenges, like working on 10-part harmonies. "We thought we'd be getting vocal coaching, but when we got to Louisiana, they said no,” Wilson recalled. “So we got the tracks, and they'd had the full track in one ear and your part in the other ear and you had to sit there and learn." To describe this process, she used the example of the Ace of Base song "The Sign," which appears several times in the film. She sang her first part, "I," followed by a long pause, then another "I," pointing out how odd it would sound to someone not hearing the full track. "It doesn't sound good when you're just singing your bit, but when it's in the group, it sounds really, really good," she said.

Wilson also auditioned for the film with an American accent, as the part was written. She planned to play Amy as American until the cast began four weeks of rehearsals. "Usually, if I'm doing an accent in a movie, I'll keep the accent and kind of the character the whole time, but because we were doing 9 a.m. to 6 p.m. rehearsals every day, I just couldn't keep it up, it was too exhausting." When the director heard her native accent, he suggested they go with that. "I was like, 'No, I want to be an actor and do acting,'" she said, affecting a bit of her American accent. Putting her trust in director Moore, she also improvised some backstory for the now-Australian Fat Amy.

Asked if she had a go-to karaoke song, Wilson offered Elton John's "Crocodile Rock," but admitted karaoke irritates her for a technical reason. "The [microphones] are always being so worn out,” she said, “and the quality of the mics are always [such] that you can't hear yourself properly.”

Pitch Perfect opens nationwide Friday.

Related: Spinoff Review of Pitch Perfect