"I was a bit of a faker, a circumstantial smoker," she argued. "I just feel like I wasn't addicted to nicotine," Stewart explained. Struggling to find the right words, she eventually gave up and added, "I just wanted something in my mouth."
Red-faced after her R-rated pun, she asked O'Brien, "Why did I do that?" O'Brien joked, "I'm glad for the Internet that you did do that."
The actress also chatted with O'Brien about the new style of filming for the vampire sex scenes in The Twilight Saga: Breaking Dawn - Part 2 where they shot just a close-up of her face. "It's nice to see your own reflection while your making 'shmexy' faces," she said sarcastically. "It's absolutely absurd, actually."
"It's got me now thinking that I want to shoot myself, just my face," O'Brien joked.
The interview was previously recorded, as Stewart is overseas attending the film's premieres. The actress walked the red carpet in a sheer, black lace Zuhair Murad bodysuit on Wednesday at the London premiere.
On the London red carpet, Stewart told Us Weekly that the fan support throughout the films has meant a lot to her. "That's honestly been, I mean, to sustain energy on one project in five years is pretty remarkable, and we wouldn't have been able to do that if we were the only fans of it," she said. "But to look over your shoulder and see a million people doing that with you is insane and amazing and contagious. Once in a lifetime."
And she was thrilled to finally play a vampire in the final film -- except for those vampire contacts.
"Those red contacts are awul -- like, tunnel vision, wallpaper eyes," she told reporters. "I think I've been sitting around for years watching everyone else do it. I've played [Bella] every step of the way as a human, so that final one made so much sense to me, I was raring to go."