Deliberate mistake: When the vortex is summoned to get rid of the monsters, other things get sucked into it. Cars, trees, light poles, other police officers. However other things or people who are more accessible do not get sucked in. For example, Phoebe hiding behind a bench, the bench itself, Phoebe's mother and a few cops hiding behind a cop car, etc.
Deliberate mistake: When the hillbilly is dragged into the cellar, the resulting explosion of blood has a much greater volume than the actual amount of blood in a human body. This is done to support the campy gore motif of the film. (01:03:20)
Deliberate mistake: When the blonde girl is doing a strip tease, she has long hair which reaches far down her back. However when they show a flash shot of her breast as she spins, her hair is only to her neck. Obviously a double.
Deliberate mistake: When Larry comes inside the house (right after Kirsty encounters the cenobites and Frank and Julia discuss getting him a new skin), he is absolutely bone dry... but we can hear a steady, heavy downpour outside when he opens the door. Seems like they added a rain sound effect in post for a creepy ambiance even though it wasn't shot with that in mind. (01:09:35)