Gallery: Actors Who Really Got Into Their Roles

Perhaps the most famous in recent memory: The skinny Zellweger gained 20 pounds to play the chubby heroine of Bridget Jones' Diary in 2001, worked the weight off to star in Chicago, and then gained it back for the 2004 sequel Bridget Jones: The Edge of Reason.

Renee Zellweger's opposite in many ways: For The Machinist, Bale dropped from 173 pounds to a startling 110 to play an emaciated man plagued with paranoia and insomnia.

For roles where her character must look haggard and unfocused (such as in Rachel Getting Married), Hathaway gets drunk the night before and shows up to work hungover.

For his incredible turn in The Dark Knight, Ledger scribbled ramblings in notebooks and pushed himself to physical and mental limits to take on the persona of the scarred, crazy Joker. No surprise, he was posthumously awarded an Oscar. (His fatal overdose came about six months before the film's theatrical release.)

Knowing that he would have to spend multiple takes strapped into a straitjacket and shoved into a mortuary drawer to aptly portray his character's torture in The Jacket, Brody decided to also spend "quadruple sessions" in a sensory deprivation chamber in Glasgow, where they were filming.

Yep, Sevigny gets a second spot on this list. Because who could forget the final scene in The Brown Bunny, where Sevigny performed unsimulated oral sex on co-star Vincent Gallo. Sevigny defended the scene when the film was released in 2003, though in a recent Playboy interview she admitted, "There are a lot of emotions. I'll probably have to go to therapy at some point."

The actor, who has immersed himself in prior roles, encountered a dilemma while playing a pothead and his twin in Leaves of Grass: To toke or not to toke. Norton, who is a big proponent of legalizing marijuana, ultimately realized that he wouldn't be able to live up to the demands of the shoot if stoned.

For Winslet, it's less about the journey there and more about the journey back: "It's like I've escaped from a serious car accident and need to understand what has just happened. When I leave a character, I have to analyse the trance through which I have just passed. It can take me several months to say goodbye to them."

At the 2011 PaleyFest, Franco's Freaks and Geeks castmate and on-screen girlfriend Busy Phillips recalled how the actor/performance artist had created a whole backstory of childhood abuse for his character, without her knowing. So when Phillips touched his arm in a scene, he screamed, "'Don't you ever [expletive] touch me again!' and threw me to the ground. I had the wind knocked out of me." She ran to her trailer crying, until she found out that he had just been going the Method route.

If you're in a movie where you're at odds with Meryl Streep, you'll probably turn in a good performance, but you won't get a friend. As the icy Miranda Priestly in The Devil Wears Prada, Streep didn't interact with co-star Anne Hathaway between takes in order to keep up the barriers between their characters. Several young actors who have worked with her, including Bryan Greenberg and Lindsay Lohan, have said that Streep would begin to improv in-character right before the cameras started rolling.