Femina ridens (The Laughing Woman) (1969)

Beautiful PR woman, Maria finds herself trapped in the home of the sinister and troubled Dr. Sayer, where she is subjected to a series of increasingly bizarre, terrifying, and degrading sex games. Sayer admits that he has murdered several women after the same ordeal, always killing them at the point of orgasm. But all is not what it seems, and through a series of twists and turns, the whole situation is slowly turned on its head.