'The Girl on the Train' Team Breaks Down the Biggest Changes From the Page to the Screen

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The Girl on the Train
has been compared to Gone Girl so many times that the biggest twist in the former's narrative would be if it was written about without a single mention of the latter. That said, forgive us for doing it one last time: when Gillian Flynn's best selling novel was turned into a movie, many wondered how the twists and turns could possibly translate to the big screen. The similarly titled and similarly sensational Girl on the Train, by Paula Hawkins, also posed a similar challenge.

"I think the biggest challenge was that I was juggling three points of view, memory, flashback, false memory and sometimes memory within memory," screenwriter Erin Cressida Wilson explains to ET of the puzzle she had to piece together.

Spoilers ahead for The Girl on the Train.

In the end, Wilson and director Tate Taylor (The Help) used the same method Flynn and David Finch did before them: sticking to the source material. For the most part, The Girl on the Train film unfolds exactly as the novel did, down to the film's introductions of the three women -- Rachel (Emily Blunt), Megan (Haley Bennett), and Anna (Rebecca Ferguson) -- via title cards.

"The book keeps switching around from point of view to point of view depending on the chapter. I had to drop that. However, I felt that opening with it would establish the three POVs," Wilson notes. "Then staying within Rachel's [POV] kept us moving steadily along. I opened with Rachel's voiceover and I tricked the other voiceovers, because they're actually not. We think they're voiceovers and then we realize they're actually talking to someone."

"I gave it a try only through Rachel's [POV], and it just felt like it lost the soul of the book," she adds. "It's really important to have this triad."

Wilson stuck to this approach throughout, making minor changes here and there that were always rooted in the text. For example, there's a passage in the book where Rachel fantasizes about grabbing Anna's hair and smashing her head into the ground, which was reappropriated for Megan in the film. ("I was like, Oh! I have to use that!" she exclaimed.)

RELATED: 'The Girl on the Train' Review: Emily Blunt Helps Prove Sometimes the Movie Can Be Better Than the Book

As for the other changes made, we broke them down with Wilson and Taylor:

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Moving the Story Across the Pond

The biggest change in the movie is relocating the story from London to New York City, though Blunt does maintain her English accent. Wilson ultimately says the movie was an inconsequential change. "I always felt that the location of this film was on the train and in her imagination. So, I didn't see it as an English book, I didn't see it as an American film," she says. "I saw it as a film about a woman on a train."

"Paula's book was not full of a ton of English slang. Of course, it has references, but it's not an overwhelmingly English book," she continues. "Changing it to an American voice and setting was very simple. And putting it up on the Hudson River -- it's so beautiful and those backyards are such a dream. You go by them and you think, Wow, they have a perfect life."

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Giving Rachel a Hobby

Book Rachel spends most of her time on the train just thinking -- obsessing over Tom (played on-screen by Justin Theroux), Megan, and her lot in life. Movie Rachel externalizes some of these thoughts by way of a sketchpad. "It was the way I started the script," Wilson says. "The script opens with her, we see someone blowing a mist on the window and then drawing into the mist and, through the mist, seeing the view out the window of the backyard over the perfect lives."

"So, she draws. It's a form of her voyeurism," she continues. "It's another way to pull her away from participating in reality and in life and it's another way to control what she sees and turn it into her own fantasies. In my script, originally she ends up writing almost a graphic novel of the entire story by the end. There was more drawing, and then eventually, I pulled it back -- I think that writing can be difficult, I preferred to see the visuals of her obsessions. Also, it tells us that she's a sensitive soul."

RELATED: Director Tate Taylor Reveals Which Oscar Winner Wanted a Cameo in 'The Girl on the Train'

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Turning Emily Blunt Into an Alcoholic You Can Root For

Book Rachel is constantly chugging canned gin and tonics, but for the film, Wilson only wanted Rachel to drink if it added to the story (and Rachel's drink of choice became vodka from a water bottle). "I wanted to use the drinking as a device for stagnancy but also a device for the blacking out, the memory loss, and the gaslight of it all," she explains. "I really made an attempt to not bring drink to lip too many times, because that can become repetitive. I also added the Alcoholics Anonymous stuff because I wanted to just have a clear delineation: Now she's not drinking, and she's making a choice to recover. I wanted that hope. And then, like a true drunk, she slips, and there's no big fanfare around it. It just happens."

Tate Taylor says that casting Blunt also changed the perception of Rachel's drinking for audiences. "They like Emily! They like Rachel!" he tells ET. "They're like, "You know what? F**k it! You deserve that beer. Go for it. Start tomorrow!" That's what Emily brought to the role."

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The Martha of it All

In Hawkins' novel, Tom has been taking advantage of Rachel's blackouts to instill false memories and gaslight her, including mention of an incident with Clara, a wife of one of his colleagues. Clara becomes Martha in the movie and plays a much bigger role, telling Rachel that Tom is "such a bad guy."

As portrayed by Lisa Kudrow, Martha also happens to be the third blonde in the movie, after Megan and Anna, but Taylor says this is purely coincidental. "I really just wanted to cast someone who you could [do a] reversal of expectation [with], who you could meet and think she's a stuck up b**ch, so Upper East Side, to go along with Tom's story," he explains. "And then when they speak, [she’s] someone who couldn't be more lovely and sweet -- that girl next door. That is totally Lisa Kudrow. Hair had nothing to do with it. Unless you think it's really smart, then you can act like I did it on purpose."

RELATED: Emily Blunt Says 'Girl on the Train' Extras Thought It Was a 'Friends' Reunion

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Uncomplicating Rachel and Scott's Complicated Relationship

Rachel's relationship with Megan's husband, Scott (Luke Evans), is far more volatile on the page, with a one-night stand thrown into the mix. In the movie, Detective Riley (Allison Janney) only insinuates they might have.

"I wanted to keep Rachel kind of pure. I wanted her obsession to remain on Tom, and I found that when I gave her sex scenes -- which I did, with Scott and with some other guy on the train -- it almost ruined the story, frankly," Wilson says. "It really took away from her purity and her obsession. I think that she's not about actually having sex with the objects of her desire or fantasy -- she's about playing around with them. If she were to have sex with Scott, she'd be a healthier person probably!"

There is a more practical explanation for another change: at one point in the book, Scott physically drags Rachel into a room in his home and locks her inside. In the movie, Scott confronts her at her apartment and never lays a hand on her.

"It became too big of a set piece, frankly. It became a little genre-esque, with her being locked in the room and then escaping. It felt tonally incorrect for this film," she says. "I felt that the threat and possibility were ultimately stronger than him turning into a lunatic. Frankly, we had to keep that for someone else."

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Deciding How to Best Use Anna

Anna, Tom's new wife and mother of his child, is one of the three POVs in the book, so you hear the events from her perspective. She has less of a presence onscreen. "The best way to keep her dangerous was to keep her mysterious," Wilson said. "Less is more."

Anna does have a major moment in the climax of the film, however: after Rachel stabs Tom in the neck with a corkscrew, Anna twists it in further to finish the job. "I think that they made it even scarier, because the murder is more brutal than in the script," Wilson reveals. "I feel like I know a lot about female rage, but Tate seems to know a lot about male rage, and when he came in and directed the male rage, he really got it."

"I just said, 'Let's go for it!'" Taylor says with a laugh. "I had two beats I had to service: [Rachel] stabbing Tom and then Anna's reaction, which is why I made Rachel's murder of Tom come quick and fast and not lackluster. [It was] a little more about the emotion of her killing Tom, not the process, and then once that was serviced, I had a lot of fun with Anna."