‘Gravity’ director Alfonso Cuarón on Sandra Bullock’s toughest scene

Imagine having to give the acting performance of your career while, at the same time, wearing a bulky space suit and pretending to float inside an abandoned spacecraft. For “Gravity” star Sandra Bullock, that was all in a day’s work.

“The film is about adversity,” director Alfonso Cuarón said during the Toronto International Film Festival last month. “Everything was a big challenge, but that was the spirit of the film.”

Cuarón’s harrowing space survival movie stars Bullock and George Clooney as a pair of astronauts marooned in orbit after their shuttle is destroyed in a freak meteor shower. Bullock recently spoke about the physical challenges she faced while shooting the 3D film, comparing the process to being a performer in Cirque du Soleil and calling the whole experience “uncomfortable” and “isolating.” But for real insight into what Bullock went through while making “Gravity,” you have to ask the filmmaker who was with her every step of the way.

"It was clear from the get-go that the actors were going to be floating in zero G," Cuarón said of the physical demands the film would place on the performers. "And to complicate matters we wanted long, fluid shots."

In order to make Bullock and Clooney appear as though they were completely weightless in the movie, Cuarón and his team had to develop a special motion control camera and rig (to hold the actor) that would simulate a zero gravity environment when combined with computer generated imagery.

"We had to keep in mind that there was going to be an actor who had to perform the whole thing," the director said. "The team were really, really concerned about how to make everything as easy as possible for Sandra."

Surprisingly, Cuarón said that the most difficult scene to shoot wasn't one of "Gravity's" many thrilling action scenes, but instead a quieter moment featuring Bullock's character Dr. Ryan Stone.

“Probably the longest shot in the whole film is a shot that’s just pure performance from Sandra inside a capsule,” Cuarón said. After realizing the seriousness of her situation, Bullock’s character goes on an emotional roller coaster of anger and despair, gets a morale boost from some unlikely friends, and resolves to survive her ordeal. “That’s not only a tour de force of emotional performance, but she was doing that while performing zero G with her body!”

According to both Cuarón and Bullock, the intense scene went through many versions before they got it right.

“We were struggling with that scene,” the director said. “Every rewrite that I tried with Jonás [Cuarón’s son and the film’s screenwriter] it sucked. She was talking to herself and it felt forced.”

Luckily, Cuarón and Bullock happened to have George Clooney on set when they ran into the problematic scene. Clooney, an Oscar-nominated screenwriter ("Good Night, and Good Luck"), offered to help rewrite the scene, and much of what ended up on screen is the result of that work.

“We were rehearsing and talking about the scene when George was on set,” Cuarón said. “One night I received this email from George: 'I gave that scene that you guys were discussing a shot. It’s not my business so throw it out or use it or use little pieces.' I sent it to Sandy and we both said ‘This guy nailed it!’”

You can see Bullock and Clooney struggle to survive the dangers of space when Cuarón's "Gravity" blasts into theatres on Octo. 4.