In Arizona, Penn wanted to film scenes of Hirsch kayaking on the Colorado River. McCandless had once canoed nearly 400 miles of the Colorado to the Gulf of California.

HIRSCH: I'd never done any kayaking. I had one day of practice, and then on the day of the scene, on our jet boat, we went right by the rapids where I'd practiced. I thought that was where we were shooting, so I said, "Why are we driving by it?" Sean looks at me and says, "That's not a rapid." And we go a couple miles down, and there's this huge, bone-crushing rapid that made the one I'd already done look like a tide pool. And Sean, being a man's man, said, "I'll go first," and he hadn't even kayaked before. He went two-thirds of the way down and just ate shit.

PENN: The only thing I could offer back [to Emile] was to be wherever he was and do the same thing he was doing. Not as well, by the way.

POHLAD: [As a producer] you're always nervous about all of it. Sean too, because he's right beside him. He never wanted to be seen as the guy taking a backseat for anything.