Kiefer Sutherland "panicked" on his first day on the set of Melancholia after director Lars Von Trier told him they'd be shooting the drama without a rehearsal.
The 24 star was prepared to run through scenes with castmates Kirsten Dunst and Charlotte Gainsbourg and admits he was stunned when Von Trier began to roll the cameras instead.
He tells the San Francisco Chronicle, "There's one constant in every job I've every done, which is you get to work in the morning... you rehearse it and you shoot it. That constant has never been broken.
"(Shooting with von Trier) I realise we're not going to rehearse it, he's just going to shoot it. I panicked... For the actor, it was the ultimate nightmare experience, because it was one of the first things we shot and everybody just wanted to be Lars' favourite. He just kept calling, 'Action.' It was like, 'What the f**k are we doing? What page are we on?'... I watched about eight unbelievable actors all feel like extras that didn't know what the f**k they were doing, and Lars liked that a lot."
But the actor insists he learned a lot about improvisation from the Danish filmmaker.
He adds, "There was an unbelievable freedom to it. What it did for me is it did deconstruct everything I knew about what I'm used to doing as an actor. I was in a moment and that was a huge education for me... It was a real leap of faith, and it was kind of one of the best leaps I've made. I loved working with him. He has a special place in my heart."