Bill Hader has spent a lot of his career smiling. Nearly ten years on SNL and a decades-long career as a comedic actor will do that. But if there's one time you don't want to be smiling, it's when you're staring down Pennywise the Dancing Clown on the set of IT Chapter Two.

The sequel to 2017's horror sensation, IT Chapter Two pulls from the half of Stephen King's novel that wasn't used in Andy Muschietti's first film. That means we're going to meet the grown up versions of the Losers we fell in love with in IT, and in a truly spectacular piece of casting Hader is taking on the role of Richie Tozier, the resident "Trashmouth," known for his ridiculous impressions and goofy sense of humor. Stranger Things breakout Finn Wolfhard played Richie in the first film (and will return, presumably for flashbacks, in the sequel), and with Hader stepping in for the adult scenes, the actor came face-to-face with one of King's most horrifying creature creations... and it turns out he couldn't stop smiling.

Hader stopped by the newly revamped Conan on TBS and had a hilarious chat with Conan O'Brien about his experiences on the film, from yucking it up on set with a full costumed Bill Skarsgard to realizing he had the exact wrong reaction in scary scenes.

"This is my first horror movie, and I'm terrible at acting scared, apparently. When I'm scared, I think I smile. Like, I get nervous and I smile... We would do takes and the director Andy Muschetti would come and he's like, 'Bill, you need to be scared, man.' I go, I was terrified! He goes, 'No man, you're smiling the whole time. What's wrong with you?' And it's true."

Of course, as any fan of Hader's Emmy-winning performance as a hitman-turned-actor on HBO's Barry can tell you (not to mention the criminally underrated The Skeleton Twins) -- Hader's got the range to pull of a lot more than comedy, and I've got no doubt he's going to crush it in the final film.

Check out the chat for yourself below (it's a lot of fun). IT Chapter 2 arrives in theaters on September 6th.