In an interview on National Public Radio, Elisabeth Moss said that none of the film is improvised. Despite the fact that some of her dialog feels spur-of-the-moment, even nonsensical, Moss said that everything she says on screen was on the page, and that it was the hardest dialogue she'd ever had to memorize.
During a Q&A at the 2018 New York Film Festival, Alex Ross Perry cited Axl Rose as the main inspiration for the character of Becky. Perry also cited the screenplay structure for Steve Jobs (2015), with its lengthy scenes that span over time, as an influence.
During the segment at the recording studio, Becky rattles off a few lines of a song about a garbage dump, as the Akergirls look on, horrified. The implication seemed to be that Becky had devolved to the point that she was improvising nonsense lyrics, but "Garbage Dump" is credited to Charles Manson.
The Phantom of the Opera T shirt that Becky wears in one of the scenes is an intentional tribute to the musical, which director Alex Ross Perry had just seen for the second time. He said it "changed my life" and that Becky was "just like this monster that lives in the bowels of people's imagination, creates music, and then kind of wreaks havoc on people. "