The great director and the movie's star Marlon Brando came up with the idea to use dairy during a graphic sex scene over breakfast and Bertolucci chose not to tell a shocked Schneider about their plans.
In a new Playboy magazine interview with contributor James Franco, he reveals, "Marlon and I decided over breakfast one morning to use butter in their sodomy scene, which wasn't in the script. I decided not to tell her - it was asking for too much discussion.
"You can see how humiliated she is in that scene. It was somewhat... strong. She was very upset with both of us afterward.
"She died two years ago and I wanted to apologise. It was a great performance, and I know you need to use any method possible to get a good shot, but maybe it was bad manners. Actors naturally feel deeply about their characters, because they're bringing life to something that's black and white, and I believe actors are writers in their films, in a way. But that film shocked Maria her entire life."