It's National Orgasm Day today (whatever that actually means) so HuffPostUK Entertainment is contributing to the celebration/discussion/campaign with its own collection of some notorious sex scenes on film.

Sex scenes on celluloid have often stirred debate, with fans discussing at length whether actors had real-life sex or were faking it. Some actors have held their hands up in pride, while others deny anything other than acting.

Check out sex - sorry, six - films below which have stirred debate and tell us which of them you think contain some real-life hanky-panky...

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  • The sex was real in 9 Songs, Michael Winterbottom's 2004, which film is often said to be the most sexually-explicit mainstream film ever released.

  • Antichrist director Lars Von Trier included real sex between stars Willem Dafoe and Charlotte Gainsbourg in this film

  • The Postman Always Rings Twice reportedly saw Jack Nicholson and Jessica Lange have sex for real

  • Sienna Miller has denied it, but an on-set insider claimed that the sex scenes between Miller and on-screen (and reportedly off-screen) love interest Hayden Christensen in Factory Girl were very real

  • "It's not about sex it's about sexuality," claims the trailer for Shortbus, a film full of real-sex.

  • Béatrice Dalle and Jean-Hugues Anglade were rumoured to have had sex in this 1986 French film.