While it's important for actors to get into character, some celebrities take it to the next level. Here's a countdown of some of the craziest stories.
Once they've landed a role, celebrities undoubtedly spend a lot of time preparing for their new project.
However, some stars go the extra mile to ensure they're fittingly in character.
Whether they're going on an extreme diet or spending hours a day rehearsing a particular skill, here's a look at some of the craziest things actors have done for a role.
Emma Stone in "The Favourite"
The 29-year-old actress, who stars as a maid named Abigail in the upcoming period drama "The Favourite," had to wear a corset for her role — and according to Stone, wearing the garment for a long time really affected her body.
"Women existed like that for such a long time, which gives you a lot of sympathy for that time period and what they were going through," the star said during a recent appearance on the Graham Norton show per the Daily Mail.
"For the first month, I couldn't breathe and I would smell menthol and it would make me think I was in a wide-open space and could breathe for a moment in time," she continued.
"After a month, all my organs shifted — it was gross and if you don't have to, don't do it!"
Christian Bale in "The Machinist"
Bale famously shed 60 pounds for his part as Trevor, an individual who suffers from insomnia, in the 2004 film "The Machinist."
Speaking to The Guardian earlier this year, the star took a look back at his preparation for the role, calling it an "amazing experience."
"When you're so skinny that you can hardly walk up a flight of stairs … you're, like, this being of pure thought," he told the outlet.
"It's like you've abandoned your body. That's the most Zen-like state I've ever been in my life," Bale admitted.
"Two hours sleep, reading a book for 10 hours straight without stopping … unbelievable. You couldn't rile me up. No rollercoaster of emotions … As soon as you start putting the food back in your stomach, the rollercoaster comes back."
Natalie Portman in "Black Swan"
During an interview on "The Late Show with David Letterman" via the New York Daily News, Portman revealed that she suffered an injury while filming the 2010 movie, which required a medic.
Per the outlet, the actress, who stars as a ballerina named Nina Sayers in the film, dislocated a rib after doing a lift.
Chris Hemsworth in "In the Heart of the Sea"
For his role in the action-adventure flick, Hemsworth maintained a 500-calorie a day diet.
"We have to shoot the really skinny stuff where we drop down to 5, 6, 700 calories a day, a good three or four weeks and it's going to be pretty uncomfortable, but we'll be together in our misery," Hemsworth told Entertainment Tonight.
He added: "I spend more time thinking about food than anything else at the moment."
A few weeks before the film's December 2015 release date, Hemsworth shocked fans with an Instagram photo of himself showing his huge weight loss.
"Just tried a new diet/training program called "Lost At Sea," he wrote. "Wouldn't recommend it. #IntheHeartoftheSea @zocothebodypro."
Ashton Kutcher in "Jobs"
Kutcher adopted a fruitarian diet while preparing for his role as the late Apple Inc. founder Steve Jobs in the 2013 film "Jobs."
However, the choice to only eat fruits, seeds and nuts, and no animal products landed him in the "hospital two days before we started shooting the movie," Kutcher told The Associated Press via Us Weekly.
"I was like doubled over in pain, and my pancreas levels were completely out of whack, which was completely terrifying, considering everything."
Shia LaBeouf in "Fury"
When the wounds on his face created by makeup didn't look real enough, LaBeouf reportedly took matters into his own hands.
"They were putting cuts on Shia and I said, 'Yeah, yeah, it looks good'," LaBeouf's "Fury" co-star, Logan Lerman, told British GQ via The Independent.
"And Shia was like 'No, it doesn't look real,'" Lerman continued. "He walks out into the hallway and says, 'Hey man, wanna see something fun? Check this out …' and he takes out a knife and cuts his face."
"For the whole movie he kept opening these cuts on his face. That's all real."
Per the outlet, along with cutting his face, Lerman noted that LaBeouf also had a dentist remove one of his front teeth for the World War II film.
Rooney Mara in "The Girl with the Dragon Tattoo"
Mara wanted to ensure her character Lisbeth Salander, a young computer hacker, in the 2011 crime-drama "The Girl with the Dragon Tattoo" matched how she looked in the book of the same name, which included eyebrow and nipple piercings.
"And I thought, She has it in the book, and she should have it [in the movie]," the actress explained to Allure.
"Because of all the tattoos and the makeup and the piercings, and the physical transformations my body has to go through, it would always feel sort of like I was in costume, even if I was naked," Mara said.
"It just felt like a good one to get — a necessary one to get."
Leonardo DiCaprio in "The Revenant"
DiCaprio won an Oscar for his performance in the 2015 movie "The Revenant," but according to the Hollywood star shooting the action-adventure movie was no easy feat.
"I can name 30 or 40 sequences that were some of the most difficult things I've ever had to do," DiCaprio, who played a frontiersman on an expedition during the 1820s, told Yahoo Entertainment.
"Whether it's going in and out of frozen rivers, or sleeping in animal carcasses, or what I ate on set," he continued. "[I was] enduring freezing cold and possible hypothermia constantly."