Why is The Revenant such a gruelling watch? A body language expert reveals all...

The setting is the uncharted 19th-century American Frontier, with Leonardo DiCaprio taking the lead as legendary explorer Hugh Glass. What begins as a story about the fur trade becomes an epic, immersive tale of one-man’s fight for survival and, ultimately, revenge.

Immersive is the key word here: this is not a passive watch. Left for dead in a makeshift grave with Leo, we’re embroiled in Glass’s almost animalistic efforts to drag himself back from the brink of death in order to seek out the man who has wronged him.

“In many ways there’s nothing worse than a passive watch,” smiles DiCaprio’s co-star Domhnall Gleeson when we discuss the experience of watching the film (because that’s what it is: an experience). Don’t expect silence in the cinema for this one. “You really feel like you’re in there,” Gleeson admits. This is, as the actor so poetically puts it, thanks largely to a “creeping sense of paranoia about the whole thing – about where the next attack is going to come from.”

Attacks come in just about every form. The harsh icy weather is an ever-present foe. The Native tribes hunt the fur traders. The fur trappers themselves viciously turn on each other and in one of the most difficult scenes to watch Glass is brutally mauled by a bear. Add in intense close up shots, blood dripping onto the screen and DiCaprio’s breath fogging up the lens and its easy to forget you’re sat quite safely on (the edge of) your cinema seat.

I wouldn’t consider myself a particularly squeamish person, but the bear scene is a hard watch. Iñárritu has kept the mechanics of it close to his chest. He wants the magic of the cinema to stay with people. And this certainly stays with you. Just when you think it’s over – bam! – along comes another fierce and furry onslaught. I couldn’t help but look away. Managing a quick peek around the cinema, I found I wasn’t the only one cowering behind my hands or hunching my body up behind crossed arms. At the end of the film, I felt like I peeled myself from my seat.

This physical reaction is of no surprise to body language expert Craig ‘CJB’ Baxter. In it’s simplest form, it’s a reaction to feeling threatened.

“Whenever fear strikes, we often feel safer behind some kind of barrier,” Baxter explains. “Whether it’s arms, a bag or scarf we need to placate our need for immediate emotional security”.

Touching your own face demonstrates a natural urge to soothe, Baxter adds, as well as acting to “dissipate nervous energy”. Most interesting, covering your mouth isn’t purely to stop actual sound escaping. It’s also, rather cleverly, an instinctive move to calm a rapid heart rate.

“With the hand held close, our breathing rate will naturally suppress, and consequently our heart rate – no doubt elevated tremendously from the initial shock of whatever caused the fear – will start to lessen,” says Baxter. “This results in a reduction in blood flow and overall bodily movement.”

As Oscar-worthy as DiCaprio’s performance may well be – and as fact-based as the tale is – we’re not in any real danger from what we’re seeing on the screen. But as Baxter notes: “The storyline may be fictitious but the physiological responses in the body are very much real.”

“We react in the above way because we become emotionally invested in the film and our subconscious mind is unable to turn off the part of the brain constantly scanning for these dangers.”

“I was incredibly moved when I saw it,” admitted Gleeson. “I knew that the story was a brutal story. Part of you is concerned it may end up being a brutal watch – that it's just an onslaught. Actually when I watched it minute-to-minute, I just found it really compelling.

“What higher compliment can you pay a film than ‘I couldn’t take my eyes off of it?’ Even if it was through this…” he grinned as he placed his fingers over his face.

The Revenant is in cinemas now