Pennywise the Dancing Clown, the demonic sewer-dweller who preys on the fear of children, may be the source of the scares in Andy Muschietti's It, but the group of middle schoolers at the center of Stephen King's timeless and terrifying story, better known as the Losers' Club, are the film's heart and soul. Without them, It would be just another empty horror film.

Of course that meant that the chemistry between It's cast of young actors would be instrumental to the film's success. Knowing this, producers arranged a 10-day bootcamp prior to the start of principal photography so that the cast could not only bond but also immerse themselves in the 1980s, when the film is set. (For Stranger Things star Finn Wolfhard, that wasn't so hard.)

It didn't take long for the kids of It to become best friends. "After the first couple of days we knew everything about each other," Wyatt Oleff (Stan Uris) told MTV News at press day for the film last month. "We were best friends. We had sleepovers. It was great."

In addition to watching '80s movies and learning how to ride bikes (for some, it was a challenge), the young cast also participated in trust exercises and acting warm-ups, including trust falls. "And people were dropped," Chosen Jacobs (Mike Hanlon) said. "Sorry Jack [Dylan Grazer]," Wolfhard jokingly added. "It was your own fault."

"We did these acting exercises that helped us get closer to each other," Jaeden Lieberher (Bill Denbrough) said. "We would look into each other's eyes for a minute, or just improvise. I felt like we knew each other forever." And yes, the group chats (there's one on every social media platform) are still very active among the Losers.

"Too active," added Wolfhard.

The cast's genuine friendship off screen translated to a easy and dynamic chemistry on screen. Their bond is what grounds the movie in the horrors of something real: the pangs of adolescence. Sometimes, the everyday trauma of growing up can be just as terrifying a murderous clown.

It crawls into theaters September 8.