40 Days and 40 Nights (which director Michael Lehmann once called "a comedy of abstinence") tells the tale of a young man who, disillusioned with meaningless sexual encounters, pledges to cleanse his system of all things sexual (including masturbation) with a vow of chastity for the duration of Lent. The problem? "He's starting to have visions," Hartnett explained, "because he's deprived himself of a well-needed wank."

The film was based on screenwriter Rob Perez's own diary recounting his experience with self-denial, which Hartnett read to better understand what his character might be feeling. Hartnett's verdict? "Just madness!" So Perez didn't last through 40 days? "Are you kidding?"

[Hartnett himself conducted an experiment -- and lasted about two weeks. He was later asked what he would give up for Lent: "Something a lot simpler than sex," he said. "Pop or candy, or something like that."]