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(CNN) - Showtime's "Masters of Sex" was one of the few first-year television shows that made the American Film Institute's top 10 TV shows of the year.
The series stars actors Michael Sheen and Lizzy Caplan, who portray real-life researchers William Masters and Virginia Johnson, pioneers of the science of human sexuality.
On the surface of the series are awkward, embarrassing moments that deal with sex and nudity, but Sheen says those are not the most difficult scenes to film.
"It's actually the challenges of being intimate with someone, being vulnerable, it's sort of an emotional and psychological vulnerability and intimacy that becomes the hardest thing to reveal," Sheen said in an interview with CNN's "The Lead with Jake Tapper."
"It's when you reveal things through the kind of mask of the character about yourself, that it feels the most vulnerable and exposing. And there was a lot of that as the series went on," said Sheen.
For more of our interview with actor Michael Sheen, check out the video above.
CNN's Jessica Metzger contributed to this report.