Imagine if your life depended on your will to break the two bones in your forearm and then cut through the flesh, muscle and tendons using a cheap, blunt pocket-knife. Think you could do it?

127 Hours (directed by Danny Boyle and starring James Franco) has everyone walking out of cinemas asking themselves that. The movie tells the true story of mountaineer Aaron Ralston who becomes trapped in the bottom of an isolated crevasse in the middle of the desert in Utah. Ralston spent over five days trying to escape before eventually performing an incredible act of the survival instinct.

During the most intense – and arguably the most talked about – sequence of the film Boyle (whose previous films include Trainspotting, 28 Days Later and Slumdog Millionaire) does not let viewers off the hook for a second. There are no cut-aways (pun intended) from the knife, the arm or the agony on Aaron’s face. In probably the pinnacle of discomfort for the audience, he has three goes at trying to cut a thin nerve strand. To reinforce how gnarly this scene is, there have been numerous reports of fainting in US cinemas… Not just average folk either; seasoned TV execs are getting treated after passing out mid-screening.

While there is no relief during this part of the story, it isn’t just that one scene that makes the film (though, granted, it is the one you’ll see when you close your eyes that night). We watch while Aaron suffers dehydration, hunger, exhaustion and more. The flashbacks to his childhood and the mistakes that led him to his predicament are told in a brilliant mix of hallucinations and dreams. Regrets, thoughts and status updates are given to his handy-cam over the days and nights, which adds to both the suspense and also sadness of his situation. And Franco plays the difficult role – almost entirely solo, playing opposite himself and rocks with a camera seemingly inches from his face – very impressively.

The film uses ambient sound to great effect. It keeps the film grounded in realism rather than having it feel like some kind of extreme sports montage. And when it comes to the gruesome task of removing the trapped limb, having that natural sound so prominent makes the experience of watching it all the more stressful. At peak points of the amputation, sounds effects are overlaid (like a gunshot as each bone breaks) which keep the discomfort at a bearable level. Just.

127 Hours opens on February 10th.