Jim Carrey had to undergo CIA training to endure 'torture' while filming The Grinch

Jim Carrey has explained the bizarre reason why he underwent CIA training in order to play the role of the Grinch in 2000 classic How the Grinch Stole Christmas.

It's not unusual for people outside of Hollywood to consult on films in order to provide accuracy. However, when you think about The Grinch, the next thing which comes to mind probably isn't the US intelligence agency.

And yet, this is exactly what happened on set of Ron Howard's adaption of the Dr. Seuss classic.

But how, you ask? Well, Carrey himself has explained exactly how this happened during an interview on The Graham Norton Show.

Here are the techniques ways Jim Carrey relied on to get through filming for The Grinch (Kevin Winter/Getty Images)

During the interview Norton asked Carrey about a rumour that he'd previously trained with the navy seals and whether or not it was true. The 62-year-old confirmed that he had never trained with the Navy Seals, but he'd needed help from the CIA in order to get into character of the Grinch.

Literally.

"When I did The Grinch, the make-up was like being buried alive every day," he explained, adding that it took 'eight and a half hours' to get into the famous green get-up.

"The makeup was like being buried alive, every day."

The extensive prosthetics quickly took a toll on Carrey, with the actor recalling how he put his leg 'through the wall' in his trailer during a moment of frustration.

"I told Ron Howard I couldn't do the movie," he added.

The actor then went on to explain that producer and 'fix-it man' Brian Grazer was called in to intervene.

Grazer decided to call in a favour from a CIA operative who had experience in training agents in how to withstand torture.

Carrey was then taught how to do a series of 'distraction techniques' to get through the feeling of being held prisoner in his costume.

"If you’re freaking out and spiralling downward, turn the television on, change a pattern, or have someone you know come up and smack you in the head, punch yourself in the leg, or smoke - smoke as much as you possibly can," he explained.

"So that's how I got through the Grinch."

Who knew filming a kids movie would be so traumatic (Universal Pictures)

It's quite a bizarre mental image to imagine Carrey smoking from a 'giant cigarette holder' so the hairy costume wouldn't go up in flames and punching himself in the leg to get through acting in a children's film.

The CIA torture methods weren't the only techniques Carrey used either, with the acting that he also listened to The Bee Gees during his hundreds of times in the make-up chair.

We can only imagine how baffling the entire scenario must've looked to an outsider.