Interlude of Lust (1981)

A blonde with long wavy hair and a slim build starts out on her knees, sucking a well-hung dark-haired guy in a dim bedroom. You can see a tattoo on her breast and a ring on her finger as she works his dick deep into her throat — she doesn’t mind the load. They move to a living room where she’s riding him on a couch, wearing nothing but high heels, bouncing hard while he grips her thighs. Camera switches to a wide shot showing her pierced nipples and his muscular frame beneath her. Later, she’s alone, close-up, wide-eyed and lit by soft dark light as a hand holds a knife to her neck — no sex here, just tension. The shift from hot to unsettling happens fast, no warning.