IT is one of the most successful horror films of all time. No matter what metric you look at -- critical reviews, fan response, box office -- IT it has blown past expectations to become one of the highest grossing, conversation dominating horror films of the era. And it hasn't even been in theaters for a week. No doubt, a huge part of that warm welcome is thanks to the fact that the creative team aligned behind the project was jam-packed with die-hard Stephen King fans with the passion to do right by the material, including director Andy Muschietti and his creative partner (and sister) Barbara Muschietti.

The Argentinian duo got their start in Hollywood with Mama, the feature film adaptation of their short, which caught the attention of support of Guillermo del Toro. Mama may not have been the record-shattering success IT has proven to be, but few films are, and it certainly set the stage, grossing nearly five times its production budget at the domestic box office and just as much overseas. But more importantly, Mama showed off a distinct sense of style, bolstered by practical puppetry, a knack for working with child actors, and a sincere beating heart beneath the horrors, all of which would become key factors in what makes IT such a special film and triumphant Stephen King adaptation.

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Image via Warner Bros.

In anticipation of IT's theatrical release, I sat down with Barbara Muschietti earlier this month to talk about adapting King's novel to film and what they have planned for Chapter 2. Candid and open, even more than you'd one can be when dealing with the secrets of a studio franchise, Muschietti was game to talk about anything from how they came up with the original fears in the film, the joy of getting approval from King -- even for those off-book changes, and how they're planning to handle the even darker tone of the adult half of the story. She also talked about how much work they put into getting the book's most controversial character, Beverly Marsh, right on screen (and how much they fought for young actress Sophia Lillis, and of course, how much she wants Mama star Jessica Chastain for play Bev as an adult. Check out what she had to say in the interview below, and for more on IT be sure to check out my interviews with Andy Muschietti, producers Seth Grahame-Smith and David Katzenberg, and co-writer Gary Dauberman.

You guys must be having a pretty good weekend after the early reactions.

BARBARA MUSCHIETTI: It's been ... Basically, from Saturday on, Saturday morning, for us, we've been sequestered and also, we were in Toronto until Thursday working on Locke and Key. So, suddenly, we get here and it's the first time we're sitting on the first interview on the junket, the journalist tells us that he loved the film and for us, it was like, "You've seen it? This is fantastic." And then, the reactions started rolling out and it felt fantastic. It's great because it's been two years of ... mountain climbing, literally.

Well, you guys nailed it. I did a set visit for this and it was cool to see all the things you were talking about realized in ways I didn't quite expect. You guys were actually very open with us on set.

MUSCHIETTI: Of course!

I realized once I saw the movie, "Oh, they told us quite a lot." So, one of the things I was really interested in as a huge fan of the books was seeing how you guys were going to work with the fears. On set, you had told us, "It's not quite the book and it's very different," so how did you guys come up with the flute lady and the egg boy and those original scares?

MUSCHIETTI: Well, that is 100% and I'll say it, and if anybody says anything different, it is wrong --That is 100% Andy. Andy basically explored the DNA of each character and brought it close to him and to his fears as a boy in the 80's, and those fears are a manifestation of his fears... and I know that because we grew up together. [Laughs]

For instance, our mom had a print of a Modigliani painting at home and actually, there's a bit of a precedence in Mama there; Mama looks very Modigliani-esque. It was something that terrified Andy always, that print, and here you see it in the form of Judith. Judith is that fear for Andy. And then, the hair, for instance, with Beverly, that was actually a combined [effort] ... I collaborated there because I felt very attached to her hair and when she cut it, I felt that her hair should come back for her. That it wouldn't be so easy to get rid of, you know, of womanhood, that it was coming back for her.

So, it's just pure creation and I think by the time we got to the film, also having read the book when we were 14 and 16, living with them for almost 30 years, we knew the characters really well, really well, so.

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Image via Warner Bros.

That makes so much sense with the painting being something from Andy's childhood 'cause it's so weirdly specific. Of course it was.

MUSCHIETTI: And it's something that actually, Stephen King, the first email he sent to Andy when he had seen the movie, the one fear he wrote back, he said, "I fucking love the woman in the painting, it scared the shit out of me," so.

Oh, that's great. Yeah, I was gonna ask about your correspondence with King. Because on the set, you guys had not talked to him at that point. Have you enjoyed opening up a dialogue with him now that you've kinda finished your work?

MUSCHIETTI: Oh man, it's been so ... He's our hero. It's like, I get teary because he's ... I remember the feeling of Pet Sematary and Danse Macabre and the magic that had, all through our teens, he would bring, every time we'd read a book. It was mind blowing. And of course, we were also constantly watching movies, but when you're that age and your imagination is so freaking fertile and you create your own worlds, there's no going back from that. So, suddenly, that the guy that inspired you to create those worlds comes and gives you a pat in the back... [makes an excited face].

That's wild. I had an occasion to do a group interview with him last month and I was like, "I need to leave the room 'cause I'm going to cry."

MUSCHIETTI: Yes, the same idea! We haven't physically met him yet and we're dying to, like just to a coffee, anything.

So what you just said about Beverly's hair and for me, I feel like her character kinda steals the whole movie. It's really complex territory that I was very nervous about, so can you talk about how you guys ... 'Cause it's still a fun horror movie, but that's really dark and real and respectful.

MUSCHIETTI: Well, we knew the thin line we were walking on, on that subject in particular and as a woman, it's something that's -- It's horrifying and also, in the book, there's such a ... It's not a dichotomy, it's the typical profile that there is abuse at home and hence, she's being bullied at school for it and it was a thin line because the minute we met Sophia, Andy saw her and said, "It's her." And we had to fight, fight, fight to get her and we got her, but he wouldn't budge. It's her, it's her, it's her, it's her. And when he started building the character with her, that line, that thin line became a lot clearer and we knew that we had an actor that could do that, that scene, it took ... We shot the bathroom scene for two weeks, it was craziness. But, the relationship with her father and those extremely creepy scenes, I have to say, evolved during the shoot. There were ... It was not easy. We found, of course, the creepiest father in history.

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Image via Warner Bros.

Yeah, good job.

MUSCHIETTI: And very ... It was important for us to find a character that you could see him down the street and he could come, or he was your plumber and you wouldn't suspect anything, but then, at home, it's a different universe.

And those two nailed it, but it was through a lot of ... A lot of thought went into that, probably out of all of the characters, it's the one that has the most thought because it's the only character that's actually dealing with an external monster. The rest have their fears that Pennywise is a manifestation of their fears and there can be a debate on the existence or not. This is a very real ...

It's in her home.

MUSCHIETTI: Yeah, a monster at home. And what was really important for us and this changed, kept on changing on the third act, was the final, final confrontation. We thought we needed that, we wanted to see that final, yes, I'm gonna be rid of this fear and the fact that Pennywise turns into him and she confronts him.

And I liked, also, that it was, like you said, it effected the outer regions, her real life as well. And I feel like there's this aspect of being a teenage girl that gets overlooked a lot where men objectify you and women are sort of threatened by your young, burgeoning sexuality.

MUSCHIETTI: [Nods] That is it. I think, we're two women and we've both experienced that, which is a very strange place to live because you're still a little girl and suddenly, there is this strange battle you're going into without even knowing and it's painful if you're alone and you don't understand what's going on, I can't even imagine what could happen. And how you choose, as a 13-year-old, 14-year-old, how you choose to solve that, that is the danger. I want to please because also, since birth, we're taught to smile and please. So, okay, I'll solve this by pleasing.

I've heard that some of the earlier versions that screened may have had a little segment that got cut or things that got tweaked a little bit. Are there a lot of deleted scenes or tweaks?

MUSCHIETTI: There are a few, it's ... There's deleted scenes that will be on the DVD version because we just love them. There's some great scenes, it's just that right now, we're at two hours and fifteen minutes, so we just could not ... It's a massive book, it's seven characters and you want to know more about their stories and we had, for instance, we had quite a bit more with the Denbrough family, with Bill and his parents because, of course, they are the ones that they have the huge trauma and we had quite a few scenes between him trying to make things better and the parents being in such grief that are unable to deal with him. So, he's very alone and thank god, he has his friends. And it's also a part of him, still believing that Georgie is alive and he needed that, he needed to go look for Georgie while he parents are in a different head space.

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Image via Warner Bros.

So, yeah, there was ... But, I'm sure that they'll all end up in the DVD because we want people to see them.

Yeah, of course.

MUSCHIETTI: It just does not have a space in the theatrical release.

Right, sometimes you gotta tighten up. I imagine, though, because so much story boarding and prosthetic work goes into the scare scenes, were there any deleted scenes from the scarier moments, or was it emotional stuff?

MUSCHIETTI: No, it was mostly emotional, believe me. I don't think of the fears, I don't think we cut any of them, it's mostly ... Yeah, I would say the emotional or even the funny ones, we had to tone down the comedy because, I mean, there are some scenes where you just, again, the thing about this film that, for me, is so important, and Andy and I fought so hard to obtain and again, this is Andy being the brain that he is. The dance in tone is such a delicate balance. And you could've gone, "Okay, this is just a little too comedic here and this is just too sad," so, there weren't ... It does take a bit of a dance, so.

Speaking of tonal balance, that's really challenging in the young version of the story and Andy has said you guys are working on part two in interviews.

MUSCHIETTI: [Laughs] Yeah, they don't let us say that, but we all want to. We all want to, that's the desire.

When you think about that story, it's even darker in some ways and it doesn't have that relief of the coming of age element. How have you guys been thinking about finding the right tonal balance with that story?

MUSCHIETTI: Well, I think we intend, we'll see how we end up because we're in the process of working, but I think the flashback situation will allow us to have a bit of that, as in reminisce. I am still in touch with who I was, even if I've forgotten for this past 27 years. That little girl or that little boy is still very much alive inside. That's one way, but also, I think there will be new things in the story. Mostly because the story as it is works amazingly in the book, because you're going back and forth in storylines. When you separate them, suddenly, they become mirrors in a way. So, we need to bring certain aspects into the story that will make it ... We cannot repeat the exact trajectory. So, there will be ... It will be implementing things that are not necessarily in the book on the surface, but are things that will allow us to bring new stuff in.

That makes sense, too, 'cause I think, honestly, everybody kinda knows the kids have the better story.

MUSCHIETTI: [Nods] But, now we have to write a great story for the adults.

Yeah, exactly. Yeah, so it makes sense that you would fill it out in some ways. And it's funny, the kids have been doing these interviews about who should play their older counterparts. Have you guys spent a lot of time thinking about who you want for those parts?

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Image via New Line / Eric Charbonneau

MUSCHIETTI: Oh, of course, it's unavoidable, I mean, we have our lists. I mean, that's no secret that we want Jess [Chastain] to be Beverly and we were campaigning for it and she's the best.

I was debating this with a friend, if like ... 'Cause it helps that the kids are relatively unknown, so you can buy into them immediately. Do you want that unknown factor for any of your adult characters?

MUSCHIETTI: I want great actors. I don't ... So, in the case of Jess, I keep on saying Jess, not because of her celebrity, but because she's Beverly and maybe I'll have to bite my tongue, but she's just ... She's perfect. But, it's not about celebrity.

Andy's very focused on physical similarities, I'm a little less focused on that part. I think we can make the leap without them being exactly the same. But, it's gonna be so much fun. And I can't really think of an instance like this, it's generally the other way around. You generally cast the kids after you've done the adults, we're doing it the other way around, so it's gonna be fun.

It's interesting, I'm sure you'll have a lot of interested parties after the film comes out.

MUSCHIETTI: I hope so, I hope so.

You guys previously said that you had thought about using the Black Spot as an opener for the sequel. Is that something you still think about or have you changed your ideas?

MUSCHIETTI: There's been several different ideas also because, again, we have to ... I think one of the greatest exercises was to bring this film down to two hours and fifteen minutes. So, this has made us realize that we have to be very efficient with time, especially if we want the kids back for flashbacks, it's a lot of movie to tell. I'd love to have The Black Spot, but it will depend on where we are, how crucial it is that we start there to tell the story.

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Image via Warner Bros.
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Image via Warner Bros.
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Image via Warner Bros. / Eric Charbonneau