"Nymphomaniac" sure has caused quite the stir without even screening in that many theaters. The latest art house film from Lars von Trier made headlines for its orgasmic posters, an unusual discount for infants and -- probably most notably -- its use of digitally added porn doubles for the sex scenes.

The unusual concept was a way to avoid filming the A-list cast featuring Charlotte Gainsbourg, Shia LaBeouf and Uma actually having sex while keeping the hardcore images that von Trier wanted for his deep dive into sexuality.

On set, the whole process was anything but sexy, according to Stacy Martin, the 23 year-old actress who plays the younger version of the main character Joe. When I spoke with her at the press day for "Nymphomaniac" she walked me through what filming a sex scene was like before it was altered.

While most the composite footage won't make it into US theaters, the uncut version of the sex scenes only featured the midsection of the actors' porn double. Everything above or below actually belonged to Martin or LaBeouf, for example.

You'd think that removing all spontaneity from a sex scene would kill any believable chemistry, but for "Nymphomaniac" every move had to be carefully predetermined.

"Basically, we would do the scenes," Martin said. "What happens is that we have to agree on a position because of the CGI. Everything has to be set, so we would do the scene with Shia or whoever it was, and we would get little black dots on our bodies," Martin said. "It was very unerotic, very technical and it gets quite boring because then they have to do exactly the same with the porn doubles. But they're having real sex, and they put the two together."

All of the uncomfortable waiting and black dot application was worth it for Martin, however, because she got to work with the esteemed director without having to become a porn star.

"It's incredible, and I can be in a Lars Von Trier movie and not have sex," she said. "It's fantastic."

"Nymphomaniac Volume 1" is in theaters now. Both installments are currently available on digital platforms.