Warhol compared his films to wallpaper. ‘You could eat and drink and smoke and cough and look away and hen look back and they’d still be there’ he once said. Many of his early silent films concentrated on the performance of a single act, such as the six-hour depiction of a man sleeping.

One of his most provocative films of the 1960s is Blow Job, which shows an extended close-up of a young actor’s face as the sexual act is performed on him out of the camera’s sight. Sections of bright light interrupt the action, perhaps representing a dissolution into sexual ecstasy. Finally, the actor slouches back with a post-coital cigarette.