How they got that weird closing shot

I've always been mystified why Sleepaway Camp's "Holy shit!" Crying Game moment looks so bizarre. I just saw the doc "Going to Pieces: The Rise and Fall of the Slasher Film"from 2006. Sleepaway Camp is praised for its unexpected reveal. The actress who played her, Felissa Rose, says that was not her at all in the final scene. They called in an 18 year old boy stand-in (the nudity is real) who wears a face mask of the actress. This is why she has only one facial reaction even though the camera is in motion. It makes for a bizarre, unsettling effect almost as surprising as the penis! Felissa Rose in that doc seemed pretty cool and knew such slasher movie trivia like some kill sequences in Friday the 13th Part 2 were derived from Mario Bava's classic giallo Bay of Blood (a.k.a., Twitch of the Death Nerve). She also loves Dario Argento's stylish gialli especially Suspiria.