In the film, the Tony Award-winning actress plays a 1950s-era woman who has an affair with a handsome mental patient (Marton Csokas) at the psychiatric hospital where her husband (Hugh Bonneville) works.
"For this movie to work, I knew the (love scenes) had to be very hot and very real. It wasn't the case of doing Hollywood cheating with a nice bit of sheet (to cover us,)" she told reporters in New York earlier this week. "I signed up for that and I thought that was right, but it didn't make it any easier to do."
Richardson said that while watching the film with Neeson during a recent screening, she "slid so far down" in her seat because she was nervous about his reaction to her sex scenes.
"It was agonizing!" she recalled, adding with a laugh that "Asylum," in theaters now, is payback for Neeson's 2004, sex-themed bio-pic, "Kinsey."
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