Deliberate mistake: There is a shot of the huge Yogurt statue that is in slow motion. You can see that the smoke from the statue is rising slower than it normally would. This was obviously done to make the shot longer for Mel Brooks' voice over to fit.
Deliberate mistake: This has the old T.V. show style "it was 6 a.m. on January 7th we ... " beginnings to the scenes. Pay attention to those times and dates. They're not even close to being in sequence. I mean days, not just times.
Deliberate mistake: Walter slips on a golf ball in the judge's bedroom and the stuntman is seen taking the hard fall. (01:19:05)
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: While the rock n' roll musical is ending, it shows the hot air balloons in the background and it shows Dave up close. He talks to himself confused, trying to figure out if he really saw his boys there or not. But if not being able to notice, wouldn't he at least hear them singing in the background as well as we can? Also, before, while Alvin and Britany were dancing together, he was trying to get to them before the two bad guys could, as if he knew for sure they were his boys and that those guys were out to get them.
Deliberate mistake: When the board member is shot up in the beginning by ED-209, in one or two shots you can see the bullet impacts happen about 1/2 a second after the shot starts (Criterion DVD version). (00:11:55)
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 Jonathan and Emma are beginning to know each other, they make their way to the wood shop, where Emma picks up an "air powered tool". The tool is a staple gun, but shoots two 3" nails close to Jonathan.
Deliberate mistake: When Michael Douglas pretends to be hurt in the field, Glenn Close says, "You bastard," and her hair is not in the sunlight. In the very next shot it is. (00:27:00)
Deliberate mistake: Proctor and Harris were surprised when they walked into the Blue Oyster and found out it wasn't a restaurant, but in Police Academy 2, Proctor apparently knew not only the bar, but the address as well.
Deliberate mistake: When Larry and the two moving men are first bringing the mattress through the doorway and it gets "stuck," the camera placement makes it pretty obvious that the mattress isn't really stuck. There's far too much wiggle room on either end for it to be "stuck." (Obviously it needs to be stuck for the scene to work... but still a weird inconsistency).
Deliberate mistake: At the end of the film, two officers attempt to surround and handcuff Joshua. Using two officers to cuff someone is NEVER done for the exact reason of what ends up happening, as Joshua manages to grab a gun from one of the officers. Only one officer would have been doing the deed in the real world, but it's clear this error in being completely against police protocol had to happen so the good guys could prevail over the villain.