`If you're going to make a movie from this book, a book that chronicled a young man's search for truth, a truth that he found lacking in his own life, you've got to be as authentic as possible."

Sean Penn's words were his mission statement for making "Into the Wild," the story of Chris McCandless' skin-shedding, two years of adventure on the road, which culminated in his death by starvation in the Alaskan wilderness.

A few of the ways the scrupulous Penn made "Wild" ring true: Star Emile Hirsch did his own stunts, including kayaking down the Colorado River.

"There was absolutely no focus on acting," Hirsch says. "I just wanted to stay afloat and not suck water. The rapids look big, don't they? When I watched the movie, I go, `Wow. That was kind of dangerous.' "

"You see that look on his face when he's standing on the shore, just before he goes in?" Penn asks. "That's Emile, contemplating something he was about to have to do." Hirsch also climbed mountains, skinned a moose carcass and lost 41 pounds, putting his weight down to 115.

"Diet and exercise," Hirsch says. "Then I had to gain it back."

His method?

"Take 5, chocolate Hershey's kisses," Hirsch says.

The movie's first scene mirrors that of the book - McCandless being dropped off on Alaska's Stampede Trail. The Fairbanks man who gave McCandless his last ride, Jim Gallien, plays himself in the movie. And you can see Hirsch wearing the gold watch that McCandless gave Gallien as a measure of thanks.

"I don't want to know what time it is," McCandless told Gallien. Penn filmed extensively in the places McCandless tramped, including the wheat fields of Carthage, S.D.; the Alaskan woods; the Colorado River; and the California desert.

(For practical purposes, the movie re-created the International Harvester bus that became McCandless's surrogate Alaskan home.)

"When I took the research trip to all these places, I tried to meet as many people as I could who had met Chris," Penn says. "What you read in the book is the real thing. He touched these people. He was still very present in their consciousness."

Read the review of  'Into the Wild' by Bob Strauss

Read about the rafting guide who got Penn's attention, Brian Dierker

Read about Director Sean Penn's process of adapting 'Into the Wild' from novel to film

-stories by Glenn Whipp