Bell plays a sadistic dominator in Lars Von Trier's new movie, which explores the life of a sex addict, and he shot some aggressively explicit scenes of violent sexual encounters with lead actress Gainsbourg.
But the director's unusual methods meant the Billy Elliot star found himself in front of the camera with Gainsbourg before the two had even had a chance to say hello.
The actor tells Britain's The Guardian, "With Lars, you literally get to the set and it's: 'Action!' And I lose my mind. Because I have no idea what I'm doing. For the last few years I've been working with very conventional film-makers. I'm used to rehearsals, finding beats and positions with directors. Lars doesn't do any of that. He records you not knowing what you're doing, to a degree.
"I hadn't said hello to Charlotte Gainsbourg before I started hitting her in the face... I really didn't, I swear to God, I didn't say a word to Charlotte Gainsbourg the entire time we were making that film.
"When they said, 'Ok everyone, this was Jamie's last day, he's wrapped, that's him done on Nymphomaniac,' and everyone gives a little round of applause, in my very short goodbye speech I said, 'Charlotte, I have no idea who you are but I'm sure you're a lovely person. Maybe I'll see you another time'. I literally hadn't said anything else to her."