A chat over tequila with director Andy Muschietti ended with a brand-new, terrifying sequence not in the book.

James McAvoy‘s first encounter with Pennywise came when he was 15, not much older than the average age of the Losers’ Club kids when they faced the murderous clown in Stephen King‘s 1986 novel It. The then teen from Glasgow, already a budding fan of science fiction and fantasy, had tackled the Lord of the Rings series a few years earlier. So reading something as “incredibly deep and dense” as King’s 1,138-page horror story wasn’t a stretch. “I didn’t find it that scary,” McAvoy says.

Now at 40, the actor is around the same age as the grown-up Losers’ Club members in It Chapter Two (Sept. 6). McAvoy plays the adult version of Bill in director Andy Muschietti’s sequel to his 2017 adaptation of the horror classic. But when McAvoy faced King’s concept of a killer clown this time around, he definitely wasn’t as blasé as he was in his youth.

“When I reread It as an adult for the film, I actually had nightmares about Pennywise in a way that I never did as a child,” he admits. Bill Skarsgård’s bone-chilling clown makeup as Pennywise notwithstanding, McAvoy’s new outlook on the story may be the same reason he keeps returning to a very particular kind of science-fiction and fantasy role: the half-goat faun Mr. Tumnus in the first Chronicles of Narnia movie; benevolent genius Professor Xavier in X-Men films; the buff, villainous Beast and his many personalities in the Unbreakable sequels. Clearly, the actor is drawn not only to a certain brand of badassery in his characters but to films that tend to transcend their genres.

With It, specifically, he found King didn’t just want to scare readers: “He’s writing about a small American town, he’s writing about death, he’s writing about growing old, growing up. And the movie is very much about that. You could argue the first movie is as much Stand by Me and Goonies and all those things as it is a horror movie.”

In Chapter Two, it’s been 27 years since the Losers made a pact to return to Derry should Pennywise ever rise again. Bill, played as an adolescent in the 2017 film by Jaeden Martell, is now a Hollywood screenwriter. His stutter’s nearly gone, but he’s “very lost and drifting through life,” McAvoy says. Bill can’t remember his childhood in Derry, nor Georgie, the little brother who died when Pennywise dragged the child down a sewer drain. After Mike (Isaiah Mustafa) calls the gang back home in the wake of another tragedy, old memories come to haunt them — some more literally than others.

“As an actor, you often put on a backstory you never [see] on screen,” McAvoy says. With It, he felt an “overwhelming sentimentality” as his own recollections blurred with Bill’s. “I’ve got these memories of my character as a young boy [from the first film],” he says, emphasizing his connection with the role.

McAvoy was Muschietti’s first choice to play Bill in the sequel, both because the director is a longtime fan and the actor looks like an adult version of Martell. Jessica Chastain, who plays the grown-up Beverly in It Chapter Two, was a matchmaker of sorts, revealing Muschietti’s admiration when she and McAvoy were working together on the set of Simon Kinberg’s X-Men film, Dark Phoenix. (Muschietti was her director on 2013’s Mama.)

Being a major King fan, McAvoy squealed internally. “You hear things like that a lot in your career from various different people, and it doesn’t always necessarily come through,” he says. “A very wise actor once told me, ‘Don’t believe you’ve got the job until you see yourself on screen at the premiere.'” A few months later, McAvoy finally got the official call.

“I think that he’s so committed to the character, to the story, and something that I cannot value enough, which is his talent,” says Muschietti, who also calls McAvoy “a real trouper” when it comes to the physical stunt work — the star strained his quads and developed tendinitis in his knees from shooting multiple takes of a grueling sequence in the third act. (McAvoy’s fine now, as the actor repeated more than once on social media and to Conan O’Brien on his show.)

In another demanding scene, a departure from King’s book, Bill chases a little boy around the same age as Georgie through a carnival’s hall of mirrors to try to save him from Pennywise. The entire sequence was shot with virtually no computer effects (Muschietti says you’ll know the small bit of CGI when you see it) and two cameras rolling simultaneously. It’s a moment that emerged over drinks — tequila, to be exact — between the actor and director.

“We were missing a vital story beat for Bill where he dealt with his guilt that he caused his brother’s death,” McAvoy recalls. “I said to Andy, “What can we do?’…and literally in 50 minutes, he invented a whole new sequence. It was never in the script, and it isn’t in the book. It’s brilliant.”

Unlike the fun-house scene, McAvoy’s next project is by the book: He’ll star as Lord Asriel on His Dark Materials (debuting later this year on HBO), based on Philip Pullman’s best-selling trilogy. “They’re completely different [roles],” he says. “That allows me, as an actor, to flex my muscles and keep interested in what I do.” Asriel, a character from a parallel reality where a person’s soul exists outside their body as a talking animal, is “so overly certain and selfish.” With the character on a quest to unlock the secrets of a mystical particle, McAvoy adds, “he’s not gonna change his world, he’s not gonna change our world, he’s gonna change all the worlds.”

You know, the usual.