Continuity mistake: After Perry and Harry leave the lake with the girl in the trunk, the headrests are missing from the front seats, but when the shot cuts to them arriving at Harry's hotel, they reappear.
Factual error: On Day 3, look at The Embrey Star newspaper when it zooms into the headline. Above the headline is the newspaper's web address, which is unlikely given the paper is from 1980.
Revealing mistake: Towards the end when Harmony calls Perry's phone as she's lying on the ground, Harry grabs the phone and looks at the caller ID to see her name. Unfortunately that's not the display showing who's calling. Anyone who has a Nokia phone will recognise that that's showing the contact list with just two entries - Harmony and a random number. The fact that it says "contacts" at the top of the screen is a bit of a giveaway.
Revealing mistake: In the party scene, when Harmony opens the Johnny Gossamer book, it can be seen at the top of the pages that the book she is reading is actually Maureen Child's "Man Beneath the Uniform".
Continuity mistake: When Harry and Perry were on a rooftop after finding out the identity of the girl in the lake, Harry was talking non-stop and Perry puts up his left hand to Harry's mouth to stop Harry talking. When the scene cuts, we see that Perry has his right hand up instead of his left.
Continuity mistake: When Gay Perry returns to toss Harry's stuff out of his car window, he drops Harry's jacket right outside the car. But when we cut to a wide shot a moment later, Harry's jacket is several feet away, as if it had been thrown.