The stars of Lars von Trier's 2013 film, Nymphomaniac — Shia LaBeouf, Charlotte Gainsbourg, Stellan Skarsgård, and Uma Thurman — all perform in unsimulated sex scenes in the film...just not how you imagine.
Producer Louise Vesth explained to the Hollywood Reporter prior to the film's release that the production had the stars simulate their sex scenes, then brought in body doubles to film the same sex scenes unsimulated. Later, in postproduction, they used digital effects to combine the two. “So above the waist, it will be the star, and below the waist, it will be the doubles,” Vesth said.