TORONTO -- Sandra Bullock says acting in the mind-blowing 3D space thriller "Gravity" was "more like being a part of Cirque du Soleil" than acting in a regular film.
Directed by Alfonso Cuaron, "Gravity" features Bullock and George Clooney as astronauts lost in space after an accident.
Its eye-popping special effects are drawing raves from critics at the Toronto International Film Festival.
At a news conference Monday, Bullock ticked off a list of bizarre contraptions that were used to create the stunning illusion of weightlessness in the film.
She cited an office chair on a hydraulic lift, a wire system that allowed actors to be manipulated by puppeteers and a bicycle seat on a pole.
"We had advisers from Guantanamo," joked Cuaron of the uncomfortable positions and long takes he made his actors endure.
"There was a little water-boarding," quipped Bullock. "It was necessary."
Cuaron -- whose previous films include "Great Expectations" and "Harry Potter and the Prisoner of Azkaban" -- said the film presented multiple challenges, including shooting the actors while they were constantly moving.
"There was a lot of careful planning and calculating," he said. "First with the choreography, but (also) ... with how we were going to shoot it. And that was the biggest nightmare, because there was no technology ... so we had to invent our new set of tools."
"It was genius what they were able to come up with," said Bullock, who wears a bulky space suit for much of the film.
The Oscar winner -- who is in every scene of "Gravity" -- clearly relished the challenge.
"I mean it was great. It was frustrating and lonely and bizarre and you had to sort of dig deep into your imagination and pray that something came up," said.
"But I loved it. I loved that I got to do it and no-one had done it before. So I really was grateful for that."
"Gravity" is due to hit theatres next month.
The Toronto International Film Festival runs through Sept. 15.
