Daniel Radcliffe and Paul Dano talk about making their weirdest movie yet

In "Swiss Army Man," Paul Dano is a heartbroken guy ready to end his life until a dead body (Daniel Radcliffe) washes ashore and launches one of the most unique buddy movies you'll ever see - and one of the most unique movies you'll ever see, period.

To say "Swiss Army Man" (opening nationwide Friday) is a special movie is a criminal understatement. In 90 minutes of I-can't-believe-I'm-seeing-this amazement, Dano's Hank goes on a journey back to civilization while dragging around the dead body he's named Manny, who becomes not just his best friend but an all-purpose tool, with his farts and erections becoming essential to Hank's survival.

Business Insider sat down with Radcliffe and Dano in New York City to talk about creating the story, the stunt you won't believe Radcliffe really did, Dano's envy of Radcliffe's flatulence, and if Radcliffe would accept the challenge to fight Elijah Wood (we're serious).

Business Insider: Paul, I think you came on the project first, right?

Paul Dano: I got involved about exactly a year before we shot.

BI: And in that time, were the directors [Daniel Scheinert and Daniel Kwan, known as "the Daniels"] trying to find the right actor for Manny, or were they always trying to get Daniel?

Dano: You know, we talked about Daniel very early on and then it was a question of when we were going to make the film and so there was one point where we were going to try to do it earlier but then we decided to wait to work with Daniel's schedule. I don't even remember when you got involved.

Daniel Radcliffe: It must have been at least six months before we started.

BI: So when it was all squared away, did you two get on the phone before shooting to get familiar with one another?

Radcliffe: Paul sent me a note just saying, "Hey, I think this movie is going to be amazing, I think these directors are amazing." But even if Paul hadn't written that I would still have been very, very onboard. Because when you read a script that is this f---ing original and out there and special, it stands out a mile, to be honest.

BI: And because it is so far from playing Harry Potter, is that an attraction?

Radcliffe: Yes and no. Far away from Potter, yes, but also that it's just far away from everything else that I've done. I don't want to get into the habit of every film I do is a comment on my relationship to Potter. If I was thinking only about it in those terms I'd be exhausted. So it was different from anything that I've done.

BI: The directors were another draw since they made the music video for DJ Snake and Lil Jon's "Turn Down for What." If you got this script about boners and farts and it's written by someone you've never heard of, you're going to throw it away.

Dano: Yeah, I think certainly we put ourselves in the directors' hands. We need the foundation, we need the script. But ultimately we're also sort of giving ourselves over to who's making the film. So it's super-important who is directing, especially with a piece like this. But the two go hand-in-hand. I don't think anyone else would have written this. And if you've seen their stuff, which I had before reading the script, when you get to that page where there's the farting jet ski thing, it works in your imagination partially because these guys have done crazy stuff.

BI: Still, you had to have been looking at each other going, "Are people going to get this?"

Radcliffe: No. First, there's no point in thinking like that when you're on set. But also it never occurred to me. It felt like, "Cool, that's what we're doing today." Every day I arrived with a sense of "How are we going to do that?" And every day the Daniels would answer that question with an amazing solution.

Dano: And I think that's why you have meetings, and preproduction, you have rehearsals. It's really important for everybody to be making the same film by the time you're making it, so I think while there were many wild things we did in the woods, by that point we were all on the same page.

BI: So there was rehearsal time before shooting?

Dano: A little bit. But I know, Daniel, you had met with them and Skyped with them. Or when you had your butt molded they were there.

Radcliffe: Yeah, we got to chat.

BI: Daniel, is it true you would send the Daniels videos of you wiggling and moving as if you were disfigured around your apartment and using different voices to get an understanding of what they wanted?

Radcliffe: Yeah, because I was on the other side of the country and it's hard for me to learn lines when I don't know what voice I'm going to be saying the lines in. So I would be sending them videos of me trying different voices and different ways of moving around. Just throwing out s--- until something stuck, basically. And eventually they would come back with, "Yeah, we like that, we don't like that, you look too articulate that way," it was just my way of having some preparation. But it wasn't until I got into a room with Paul that it all made sense.

BI: How much did you guys have to clean up your dialogue in postproduction? I would imagine the singing and other lines would be hard to get in the woods.

Radcliffe: I think cleanup is the right word because most of it we did some version on set. At one point we did record a version of "Montage" in the back of our sound mixer's car on our last day of shooting. But a huge amount of stuff was done practically on this film, more than you'd think.

BI: Paul, did you realize before shooting started that you would have to spend most of production dragging around Daniel?

Dano: You know, not really. I mean, yes, it's on the page -

BI: But it's not like you're working out in the gym before production began.

Dano: And I regret not having done that because I suffered, just my stamina. I thought every day, "The next time I do a film I'm going to get in shape," because any film requires some type of endurance and it's funny how there are some things you overthink. Like when you're preparing for something in the script, and some things you figure, "Yeah, we'll figure that out [on set]," because I can't figure it out on my own. I never really totally understood what it would take. [Laughs]

BI: So, Daniel, give a sequence where people will be shocked it's you and not a stunt double.

Radcliffe: The opening [of the movie].

Dano: When Manny washes ashore?

Radcliffe: No, the opening when Paul is riding me across the waves. There's one shot where Paul is pulling back on my tie and there are no visual effects, that is both of us in the water at the same time. That's me desperately not trying to blink because the saltwater was just hitting my face.

BI: You're being serious.

Radcliffe: I'm being absolutely serious. 

BI: So what, you were on a board?

Dano: Board. Daniel. Paul.

BI: Wow.

Radcliffe: It was wide enough that I could lay on it and then Paul was on my back and they dragged us along the side of a boat.

BI: Did you have to talk your people into letting you do this? Because all I'm thinking right now is insurance issues if you got hurt.

Radcliffe: I said to the Daniels very early on, "Can I do all of my own stunts?" And I think they were just relieved that they had an actor say that because they knew they weren't going to be able to afford a stunt double for the whole thing. So I had a stunt double for a couple of scenes and that's really it. And same for Paul - we did a ton of it ourselves. But that was one of the things that was exciting about it.

BI: You guys spent a lot of time together. What did you learn about each other that surprised you?

Radcliffe: Paul is an excellent basketball player. And this is coming from a truly terrible basketball player.

Dano: Yeah, at the Daniels' house they had a basketball hoop and that's where we would rehearse sometimes. That's a nice way to loosen up and come up with ideas. Get out of your head. But what surprised me was the method that Dan had to produce gas on set.

Radcliffe: [Laughs]

Dano: It's a tough thing to learn how to do.

Radcliffe: It takes some skill.

Dano: Growing up I had a cousin who could make himself fart on command. I always wanted to and I couldn't do it. So when Dan did it I was like super-impressed that he was able to do it.

BI: I'm going to go off-topic for the last question. Daniel, there's a festival called Fantastic Fest and one of their traditions is to do a debate that ends with a boxing match. Your film "Horns" played there a few years ago and I was told that year the festival tried to get you and Elijah Wood to do a Frodo versus Harry Potter boxing match. Elijah told me at the festival, "It might happen one year - you never know." I want to know what your response is to this.

Radcliffe: Here's the thing, I should say no, but the competitive part of me is finding it really hard to not just say, Yeah, I think I would beat Elijah Wood in a boxing match. But we'll see. You set it up. I've met him, he's a very nice man - who am I kidding? [Slams down his lighter on the table.] I'd love it.