Moviemaker Lars Von Trier invited his friends to recount their craziest sex encounters and adventures and used some of the bizarre stories in his controversial new movie Nymphomaniac.

The Danish director sat down with adventurous friends and acquaintances before he started shooting the film and used their tales for inspiration.

Asked to reveal one of the real-life stories that made it into the film, he tells Rolling Stone magazine, "(There's) the bet that the two girls have about who can f**k the most men during the train trip, and the winner gets a bag of M&Ms."