[Editor’s note: The following contains spoilers for IT: Welcome to Derry.]

Developed for television by filmmakers Andy Muschietti and Barbara Muschietti and co-showrunner Jason Fuchs, the HBO series <em>IT: Welcome to Derry </em>serves as a prequel to IT and IT Chapter Two, delving deeper into the origins of the entity that permeates through the quaint town of Derry. Set in 1962, no one is safe from the cycle of fear and terror as it infects and forces everyone in its path to question whether what they’re seeing is real or if it’s the sinister shape-shifter. Having come face-to-face with Pennywise the Dancing Clown in the sewers hasn’t deterred Lilly (Clara Stack) from wanting to use the dagger that was formed to kill the entity, but the rest of the new group of Losers – Will (Blake Cameron James), Rich (Arian S. Cartaya), Ronnie (Amanda Christine) and Marge (Matilda Lawler) – aren’t so keen on that idea. As kids and adults alike are forced to face their traumas, the entity isn’t the only evil lurking in Derry.

During this interview with Collider, co-stars Stack, Christine, and Lawler discussed being terrified by Bill Skarsgård when he was on set in the Pennywise costume, shooting the movie theater sequence at the beginning of the season, Marge trying to destroy her own eyes, Ronnie’s gross birthing scene, and how they felt about the way the season plays out.

Pennywise the Clown Terrified the Young Cast of ‘IT: Welcome to Derry’

“You can’t prepare for that.”

Collider: What was it like for you guys, the first time that you saw Bill Skarsgård on set as Pennywise? It’s one thing to know what he’s going to look like, but I would imagine it’s very different when you actually see him in person.

MATILDA LAWLER: I definitely was mentally preparing myself to be horrified by Bill, but you’re right, you can’t prepare for that. It’s an entirely unique experience that I cannot describe with any other word but terror. He’s just so imposing. All the elements combined, with the physicality, costume, makeup, wardrobe team, and prosthetics team are phenomenal. It’s also Bill and the energy that he brings. He is a nice guy off set, but when he’s Pennywise, you feel that terror and it is indescribable. It lives with me.

AMANDA CHRISTINE: I agree. It is definitely indescribable. It was definitely very scary to work with Pennywise. They kept him top secret. They kept him away from us until we got to that specific sewer scene. It was really cool to meet him and just experience that with him. He takes the character so seriously and really embodies being Pennywise. It was just really cool to experience that and really scary too. That reaction you see is our real reaction.

CLARA STACK: The reaction in the series is our genuine reaction to seeing him for the first time. Bill really brings such an incredible energy to set and he embodies Pennywise amazingly. He truly brought fear and stakes. When we saw him for the first time, we were all shocked and scared but also in awe. Seeing him on screen versus seeing him in person right in front of you with hair, makeup, and costume was intimidating yet super cool.

Clara and Amanda, what was it like to shoot the movie theater attack? Amanda, your character is a little bit more of an observer in that sequence, but what was it like for the two of you? What was the most challenging part of that whole sequence?

CHRISTINE: Honestly, for me, because I was an observer in the movie theater scene, we filmed it in blocks. Sometimes we filmed together, and then sometimes it was just the kids who were in the theater. That was definitely a different experience but also fun because that scene was one of our first big scenes. It got real quickly. Reading about that scene was so cool since Ronnie loves film and she’s a film addict. I had to learn how to put film into a camera which made it a fun experience. The end of episode one was iconic.

STACK: Filming that scene was so much fun! You asked about challenges—one exciting aspect was balancing performance and emotion while focusing on blocking. It’s such an action-packed sequence with so much going on with all of us kids. Getting into a vulnerable place while feeling fear while ducking under seats or climbing over them or running out was super fun too. Honestly, I loved getting drenched in blood while screaming—it was a blast!

Clara, that moment with your character standing in the theater lobby just holding Susie’s severed hand is hauntingly heartbreaking.

STACK: It was fun filming but definitely shocking—a great end to episode one.

Matilda Lawler Breaks Down That Scary Moment When Marge Tries to Hurt Herself in ‘IT: Welcome to Derry’

“I just have so much sympathy for Marge.”

Matilda, what was it like for you during episode four’s intense sequence with Marge’s eyes? Obviously those aren’t your real eyes, but how did you find both physicality and emotion during such an intense scene?

LAWLER: Who says those weren’t my real eyes? Just kidding! It was trippy! Marge goes through intense emotions during that scene. I have so much sympathy for her as she progresses through it all in woodshop. It was very intense—I lost my voice from screaming so much that week! Our acting coach Mr. Ben supported me greatly that day by encouraging me to keep my energy up while performing alongside my fellow actors who lifted me up during this gory prosthetic challenge.