The Carry on Sargent (1972)

Carry on Sargent AKA Angela's Foursome is the film which once and for all exposes the film processing house racket as a hotbed of sin and vice. When a struggling company starts taking on pornographer clients, they attract the attention of a hardnosed hillbilly cop who's on the prowl for "dirty Commie stuff from Moscow." They make a short film which hyp-no-tizes the cop into believing that porn is good (a process soon to be adopted for all SWV tapes) and then to seal the deal, the hypnotist bangs the lab technician (in slow motion). "Wonderful! Just wonderful!" barks the hoodooed porker. We couldn't agree less.
Important note: there is no actual foursome in Angela's Foursome.