Haunted by the non-fictional ghost he was portraying, Steve Zahn – who previously had been typecast by Hollywood as a comic reliever – lost 40 dead-serious pounds for Rescue Dawn to walk the same footsteps of a POW four decades earlier.

“Once you get past the wheat detox, losing the weight was more mental than physical,” Zahn said in a Chicago interview with Adam Fendelman. “I weighed myself for the first 20 pounds and then stopped. The closer I got to the movie, the more it became about Duane.

“I had his picture all over the place – on my fridge and everywhere – so I was always reminded. If I wanted to cheat and eat, I had to look at his face. I didn’t cheat because I wouldn’t be telling the truth. It’s a weird state when you get to that spot where your body has changed that much. It’s like you just woke up.”

Though safely nestled in our Chicago hotel room, you could tell Zahn wasn’t acting when he delivered the words “his ghost is still out there, man” with eyes lost in the distance and his mind evoking the impenetrable Laotian jungle that was his set. It was as close as an actor could get to war-inflicted, post-traumatic stress.

With the jungle the cast’s true prison, director Werner Herzog made the environment just as much the film’s main character as Zahn, Christian Bale, and Jeremy Davies. Zahn added: “There were thorns and bugs and snakes [galore]. I’d be on set looking at a banana spider and think: ‘If that thing bit me, I’d really die.’ In many of Werner’s films, the environment is the main character.”

Bale portrays Dieter Dengler, the only American to escape a POW camp in the Laotian jungle. After months of calculating his death-defying getaway through some of the planet’s most ferocious wilderness, the renegade blazed his own route to freedom. He exploited the most primal qualities of evasion, endurance, tenacity and courage to find his way home.

Zahn, whose character mirrored Bale’s side by side, says he was inspired to haul himself out of bed at 5:30 a.m. every day in large part because of the opportunity to work with Bale.

“Christian is the real deal. He’s all those things you’re supposed to be when you’re a great actor. He’s simple, direct, intense and one of the funniest mother (sic) I’ve ever worked with. Damnit he’s funny,” Zahn said. “What we were doing could have been difficult. We didn’t need to be reminded that we were hungry and barefoot and POWs when the camera was rolling.