By Nick Romano
Updated July 30, 2016 at 04:02 PM EDT
Credit: Clay Enos
  • Movie

While Suicide Squad is filled with CG, many moments are not, including Margot Robbie‘s underwater fight. The Harley Quinn actress told Jimmy Fallon on The Tonight Show she learned to hold her breath for five minutes, even though the scene required she do so only for one.

“I worked with this amazing free-diver, and he came in and I did four sessions with him. His name’s Kirk,” she said, adding that she called him Captain Kirk. “It’s all about lowering your metabolic rate…You kinda, like, meditate underwater. It’s what free-divers do, but it’s amazing.”

Admitting to her competitive nature, Robbie described how she would try and hold her breath longer than her stunt double. “I got to five minutes and I was like, ‘You know what? This is above and beyond what I thought I’d get to. I’m good, I’m good with five.'” She says she tried pushing it even further when her double got to five-and-a-half minutes, but she was advised against it.

Watch Robbie’s interview with Fallon in the video below.

Suicide Squad debuts in theaters on Aug. 5.

Suicide Squad

  • Movie
  • PG-13
  • 130 minutes
  • David Ayer