In the highly anticipated, big-screen adaptation of "The Perks of Being a Wallflower," Emma Watson, Logan Lerman and Ezra Miller play a trio of friends who deal with some heavy issues over the course of their friendship, from loss and homosexuality to addiction, love and depression.

High-school seniors Sam (Watson) and her stepbrother, Patrick (Miller), take a new-to-the-school freshman named Charlie (Lerman) under their wing in the flick, which, despite being set in the 1990s, tackles issues that are timeless. So it was no surprise when the castmembers admitted during Tuesday night's (September 18) "MTV First: The Perks of Being a Wallflower" that some of the rawer, more emotional moments were sometimes difficult to shoot.

"I feel like we had trouble on some really easy scenes. Like, you remember when we were doing the last scene in the diner?" Miller said. "For some reason, we were just all tired and it didn't feel right again and again."

"I remember, though, it was something tonally," Lerman added. "We were trying to figure out like how to play this scene."

After presenting an exclusive clip from "Perks," the cast further opened up about making the Stephen Chbosky-directed film, which opens on Friday. (The director also wrote the novel the movie is based on.) Continuing on the topic of challenging scenes, Watson noted that her first kissing scene with Lerman was the one she struggled with most before hitting the set — and not because she didn't want to kiss Logan!

"I mean, when I read our first kiss scene, it's so epic. It's like the most beautiful scene I've ever seen written on a page," she said. "And it was like, 'Oh, we're going to have to kill this one!' Like, it's so good, I wanted to do it justice. And it's so emotional and we're both so vulnerable in it, but the main thing was I get to do it with Logan," Watson added. "He makes me feel so safe, so it's going to be fine, which made it fine."

Knowing that the smooch would be with Lerman put Watson a bit more at ease, but Logan told MTV News' Josh Horowitz that he found the scene "nerve-racking," especially in front of the crew who watched it all go down: "Those scenes are always hard to do when there's 15, 20 other people in the room."

Share your thoughts on the MTV's "Perks" live stream in the comments!