"Barbie" writer/director Greta Gerwig wanted to get reaction to her film in real time.

Gerwig hit theaters during the blockbuster film's opening weekend in July, where she revealed she would stand in the back to observe audiences reacting to the movie.

"I went around to different theaters and sort of stood in the back, and would then also turn up the volume if I felt it wasn't playing at the perfect level," she said at a panel talk at the BFI London Film Festival, according to The Hollywood Reporter.

Gerwig added that making the movie was "the most joyful" time she's ever had on a set."So, I thought, if I can make a movie that is half as fun to watch as it was to make, I think maybe we've got a shot," she said.

Gerwig has since become the first solo female director with a billion-dollar movie. ("Barbie" was produced by Warner Bros. Pictures, which like CNN is part of Warner Bros. Discovery.)

She also revealed she is in the "process of writing" at the moment, although she didn't reveal exactly what the project was. She is set to direct two "Narnia" movies, based on C.S. Lewis' "The Chronicles of Narnia" book series.