The actress sheds her wholesome image to play the late porn legend in Lovelace, which also stars Peter Sarsgaard as her onscreen husband and manager Chuck Traynor.
In one scene, Seyfried was asked to simulate a sex act on a frozen ice pop as her character prepared for her infamous role in adult movie Deep Throat, but she admits she held up the shoot because she was giggling hysterically.
Seyfried tells Vanity Fair magazine, "We were doing a scene where I was supposed to be going down on Peter Sarsgaard. We used a Popsicle, and I had my arms covering the Popsicle.
"It was footage that he was going to show the Deep Throat guy, to get her into the movie, to get her cast. I was laughing hysterically throughout. I couldn't stop laughing."