Jon Bernthal was stunned by Shia LaBeouf's horrific method acting techniques before film

Jon Bernthal admitted to his surprise at Shia LaBeouf's rather gruesome method acting techniques before they started filming together.

But, over time, The Walking Dead star grew to admire his co-star's dedication to his craft.

LaBeouf has changed drastically since his Transformers days, having starred in a string of indie films including Lars Von Trier's Nymphomaniac and Honey Boy.

Method acting, whereby actors immerse themselves in a role, whether that be physically, mentally, emotionally or all of the above, in order to deliver a more authentic experience, is certainly a divisive approach.

Some believe it adds to a performance, while others express concern over the extreme lengths some take it to.

A prime example in the latter camp is Christian Bale, who ended up in hospital after losing so much weight for The Machinist.

Nonetheless, it's a technique LaBeouf has dabbled in.

Even if he doesn't label himself as 'the method guy', he certainly went all in for the 2014 movie Fury, which centres on US tank crews fighting in Germany during the final weeks of the European theatre of World War II.

To get into the mind of his heroic gunner Boyd 'Bible' Swan, LaBeouf prepared in a number of gruesome ways – including pulling his own tooth out.

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Bernthal, who played tank loader Grady Travis in the film, spoke about what it was like working alongside him while appearing on an episode of The Joe Rogan Experience.

"Shia at the time, he was a guy that, you know, when we did Fury together, that was such a wild experience," he said.

"And he was this guy who came in, he pulled his tooth out because he thought his character shouldn't have a tooth.

"He cut his face, he didn't shower for eight months."

Initially, he was wary of LaBeouf, wondering if it was just performative – but this all changed when they started shooting.

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"At first, when I met him, I was like this guy's just f***ing loud, you know? He's wearing his process on his sleeve, showing everybody how hard he's working," he added.

"But what I found after the eight months of working with him was somebody who – and it's just my own [opinion] – this thing is every bit as vital to him as it was for me.

"I found a real partner, I found a real kindred spirit. I found that he was willing to risk it all for the work."