IT Chapter Two is poised to be one of the biggest films of the year, which is pretty good considering that the horror movie doesn’t come as part of a superhero franchise and isn’t a re-do of an animated classic. It is, however, a star-studded sequel that caps off the adaptation of Stephen King‘s story about a group of small-town kids who battle an ancient evil in the form of a shape-shifting clown. Leading the charge for the adult Losers who return to Derry is James McAvoy‘s Bill Denbrough. He’ll be dealing with more than the revitalized Pennywise in this sequel, as he explained in a chat with EW.

Most interestingly from this conversation, which ranged from McAvoy’s first time reading the tome as a teenager and his more recent reaction to reading it again as an adult, to how he landed the lead role opposite Jessica Chastain, is how he and director Andy Muschietti came up with a whole new sequence for the film that wasn’t in the original book. It’s decisions like this that separate true adaptations from scene-for-scene translations but can also make or break a movie. So what exactly is this new addition? Spoilers ahead.

If you’ve seen the film’s trailer, you’ve likely already seen it. The sequence has Bill running through a carnival’s hall of mirrors in order to save a kid from the clutches of Pennywise; it’s also the likely scene where McAvoy injured himself. Here’s why they added that scene, followed by the how (which involves tequila, obviously):

“We were missing a vital story beat for Bill where he dealt with his guilt that he caused his brother’s death. 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.”

The sequence, which was shot with very few computer effects (except a tiny bit of CG work that will be obvious to audiences), included two cameras filming simultaneously. Hopefully there will be some behind-the-scenes footage of how it came about. As for the genesis of the scene itself? That came from McAvoy and Muschietti chatting about the movie over tequila, which sounds like a pretty fine day at the office to me.

It Chapter Two also stars Chastain as Beverly Marsh, Bill Hader as Richie Tozier, James Ransone as Eddie Kaspbrak, Jay Ryan as Ben Hanscom, Andy Bean as Stanley Uris, and Isaiah Mustafa as Mike Hanlon alongside original Losers Wyatt Oleff, Jaeden Martell, Sophia Lillis, Finn Wolfhard, Jeremy Ray Taylor, Chosen Jacobs, and Jack Dylan Grazer who will reprise their roles in flashbacks. Look for it in theaters, including IMAX screenings, starting September 6th.

Here’s the official synopsis for IT Chapter Two: