From the book "Sean Penn: His Life And Times" by Richard T Kelly
About Viggo and Indian Runner :

Sean Penn: "I was over at Robin's little house in Santa Monica Canyon, waiting for her to get dressed for a date. The television was on, sound off, and I saw a face: he was only a cameo in a movie (Fresh Horses) , but I saw the face that I'd had in my head when I wrote Indian Runner. He had something, an angularity, a severity to his handsomeness that I perceived as being like Frank. So I watched the movie through, and I called Don [Phillips] and said, 'Find out who he is.' "

Don Phillips:"We sent the script (Indian Runner) to Viggo...he was our man and we were off and running."

David Morse:
"During the rehearsal period, Sean really encouraged Viggo & myself, and Valeria and Patrica (Arquette), to spend as much time together as we could, to really blur the lines of our professional relationships and make them more intimate. Se we'd go to the county Fair [Omaha] as a foursome and so on. We all wanted this authenticity...."

Sean Penn:
"I had written that Frank steals a car and intentionally goes into a wealthier neighborhood..robs a gas station and abandons it by the side of a road. Mike asked me, "Why does he go to a rich neighborhood?" I said, "you know..." and he said "Well, if it's resentment towards the rich, why let the rich kids get their car back? Just burn the F'ker." I said "Yeah!" And that happened to come at an imp't time for such a visual in the movie."

David Morse:
"Do I think Frank and Joe are two sides of Sean? ...I would say yes, I do"
"Viggo and I were going to rehearse for rtwo weeks, but we were only going to rehearse our big scene in the bar. ... during those 2 weeks, I have a feeling it was harder for Viggo because Sean identified more that that role and he would really try to push him to do certain things. But Viggo just kept holding back. He never really DID the scene in those two weeks."

Sean Penn:
"Viggo is, by nature, a very poetic character: he IS a poet, and a painter. And some of his poetic nature was very good for the part, in the moment of tenderness with Patricia. but I did find that when he was photographed head-to-toe, some of the danger of Frank would go out the door: Viggo's inherent kindness as a guy showed in a sort of languid movement. And that was a lesson for me about what parts of people express themselves without trying. So he did some work...to try to overcome that...I needed an edge in that space from head to toe, there was a clear and present danger.

David Morse:
"I think Sean was still a little nervous going into that bar scene...and something happened, it crystallized and suddenly Viggo was on fire.

Sean Penn:
I think I stimulated viggo's temper. And as i remember, I think I got a little personal. But I think he was professionally responsive, he knew where to go for what I was looking for. When you're abusive to an actor, it's one thing - when you're abusive to a character, it's another. And I think I found it was helpful to both of us to raise my own tempo a little bit, and get in the same place as him, share the vibe...."