After Meryl Streep signed on to star in The Devil Wears Prada, the Oscar-winning actress invited director David Frankel, producer Wendy Finerman, and screenwriter Aline Brosh McKenna to her New York home to discuss the script, which was based on the bestselling novel from Lauren Weisberger.

“We sat with her for a long time, maybe four or five hours, and went through it,” McKenna told V.F. Hollywood on the phone earlier this month. “I don’t think I’ll be surprising anyone when I say she was incredibly smart about the script and incredibly smart about the character. She really stressed the lack of vanity about Miranda—that Miranda was really focused on her work and was under certain pressures, as a woman in that position of power . . . I do think a lot of female bosses struggle with people thinking they’re a bitch, or they’re cold, or they’re difficult.”

In the weeks afterward, Streep transformed herself into the fictional editrix of Runway magazine—carefully choosing character traits for Miranda that the actress had encountered over the years: Clint Eastwood’s soft manner of speaking; Helen Mirren’s haircut; and Mike Nichols’s delivery. By the time McKenna showed up on set for the first time, while the crew was filming a scene inside Priestly’s townhouse, Streep had done a 180 and become the icy villainess whose insults still send shivers down audience’s spines. And even though McKenna had spent hundreds of hours with the character during the writing phase, the screenwriter found herself frightened by the extent of Streep’s conversion.

“She was terrifying,” McKenna recalls of the first time she saw Miranda Priestly in the flesh. “The first scene I saw was when she turns around to glare at Andy from the top of the stairs. I was so terrified by her look alone that I threw my arm out in front of the director like we were in a car wreck. I was so scared.”

During the course of our conversation with McKenna, the screenwriter (27 Dresses, We Bought a Zoo) shared some other fascinating behind-the-scenes details about the beloved comedy. Among them:

The Famous Cerulean Monologue About the Importance of Fashion: Entirely Made Up

Miranda Priestly schools Andy on the importance of fashion during one designer-filled diatribe about historical moments in the industry. But McKenna admits that this particular monologue was not fact-based: “All of the stuff is made up,” she laughed. “It was funny because somebody wrote an article saying, ‘They didn’t show this color on this day.’ It really made me giggly because I couldn’t use real examples because, first of all, we had to pick a color [for Andy’s “lumpy sweater”] that would work onscreen and blue was going to be the best color to use, so we kind of worked from there. I mean, I’m sure there were cerulean collections, but the way we talk about it in the movie, all those references are made up.”

Stanley Tucci’s Character Was Going to Be Nicer Until a Fashion Insider Said that Wasn’t Realistic

“Someone actually said to me, ‘No one is that nice. No one has time to be and there’s no reason to be.’ It was good feedback because it took the wind out of Nigel, who could have been a more clichéd, fairy godfather-like character. The fact that he’s so hard on her in the beginning . . . she really earns the closeness that they have at the end. I think the most important thing about his character, in a way, is that Miranda screws him over at the end, and he accepts it because he accepts that she’s the queen of his world and that someday, soon, he might get what’s coming to him. It’s one of the real signs to Andy that if she stays in that world, she’ll never get away.”

Meryl Was Very Invested in Finding the Truth in Her Character

“Meryl is someone who has no vanity about her performances and isn’t concerned about being likable,” said McKenna. “She was more concerned about getting to the pith of what made this woman tick. One thing I remember her saying to me is that Miranda would be the calm at the center of the storm. She might inspire frenzy in others, but she, herself, had this ability to maintain a calm. It’s one of the reasons that she’s terrifying to people because things that would concern and upset other people, she doesn’t let them get to her.”

Miranda’s Insults Come From an Unlikely Inspiration

“I love insults,” explained McKenna. “I grew up watching Don Rickles with my dad, and that was a huge influence. It allowed me to channel parts of my own personality that maybe I normally need to keep hidden.”

McKenna came up with a few insults before she even pitched the film, one being the dig Miranda makes to Andy: “Take a chance. Hire the smart, fat girl.”

“One of the things that’s very palpable about fashion is that it’s very hard to be overweight,” McKenna explained. “It’s a world where being thin is prized, partly because of the sample sizes floating around. I thought that her describing Andy as a fat person says a lot about the values of that world, where anyplace else Andy would be considered incredibly skinny, and, in that world, she’s considered kind of portly. That seemed like an important way to differentiate them; that they live in separate worlds.”

Miranda Is Still Fresh in the Mind of McKenna

“I could write just a page of dialogue, still, to this day, of Miranda walking around insulting people,” said the screenwriter. “It just really stuck with me, and I feel like it would be fun to write just Miranda standing in line at Shake Shack, or anything, but picturing her doing that is always funny. One of those things that’s enjoyable about her is that she allows us to sort of channel some side of ourselves that we’re always repressing, where you tell people exactly what you think of them.”

McKenna Has an Idea Where Andy and Miranda Might Be Today . . .

“I think that Andy’s probably still a journalist,” said McKenna. “For some reason, I picture her being in Europe somewhere with some fabulous European boyfriend. And I think that Miranda Priestly is exactly where she was, but maybe moved up a few levels and has deposed Irv, who’s her boss in the movie. I think she’s had him assassinated.”