In fact, he went so dark one night that he stalked a woman on the train, in efforts to get into his character's mind.
"I did do a couple of things to try to get inside [his mind]. On the tube, which is our underground system," he told the Los Angeles Times.
Dornan stopped himself for a second, before asking, "Can we get arrested for this? Hold on ... this is a really bad reveal. I, like, followed a woman off the train one day to see what it felt like to pursue someone like that."
Dornan didn't get too close so that she didn't notice he was following her.
"It felt kind of exciting, in a really sort of dirty way," he added. "I'm sort of not proud of myself. But I do honestly think I learned something from it, because I've obviously never done any of that. It was intriguing and interesting."