Greta Gerwig recently spilled a surprising secret about her blockbuster movie, Barbie. The director, 40, revealed that she opted to do her own research during the film’s opening weekend in July by hiding in the back of theatres to witness the audience’s reactions first-hand. “I went around to different theatres 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 recalled during a screen talk on Sunday at the BFI London Film Festival.