By Andrea Towers
October 15, 2015 at 03:39 PM EDT
Caitlin Cronenberg

Part of the magic of Room — Lenny Abrahamson’s adaptation of Emma Donoghue’s best-selling novel of the same name is the chemistry between Brie Larson (“Ma”) and co-star Jacob Tremblay (“Jack”). So how did the 26-year-old forge the important bond with her much younger screen partner?

“We met in Toronto three weeks before we started shooting, at a pizza parlor for lunch,” Larson told Vulture in a recent interview. “He had these little Star Wars Lego figurines, and so I started asking him about Star Wars.”

Larson went on to explain that, “it’s a tricky thing, those first initial meetings, because they really are important … you have to let it happen.” The actress revealed that after the meeting at the pizza parlor, Tremblay invited her over to play with his Legos. “I went over that night and played with him for maybe an hour,” she revealed. “He was mostly quiet, but every so often he would ask me, ‘What’s your favorite animal?’ ‘I like red pandas.’ ‘Hm.’ He’d really take in all of my answers.”

While the story of Room presented its own challenges for the actors, according to Larson, bonding with Tremblay was where the real pressure was centered. “I remember walking down the hallway thrilled, just elated,” she said, reflecting on the aftermath of their first meeting. “I had never wanted to be accepted so badly by anybody as I wanted to be accepted by him. And then I was, laughing to myself thinking, He’s not thinking about this … He’s not losing sleep over me, but meanwhile, I was quite stressed.”

Room opens in New York and Los Angeles on Oct. 16 and nationwide on Nov. 6.