Deliberate mistake: When the two assassins enter Leo's bedroom and try to gun him down, the one on the right has left his tan overcoat open. He's the one that escapes from Leo initially. Shortly thereafter, Leo guns him down, firing up into a second story window. At this point we see that the assassin's coat is now buttoned up, probably to conceal the numerous squibs used in his death scene. (00:41:00)
Deliberate mistake: There is just too much movement and detail in the synthetic skin masks. Peyton lost a large portion of his face in the explosion, and cannot make much expression with his own face, but somehow he can make the masks move perfectly just like a real face.
Deliberate mistake: When the terrorists shoot a man in the church and he falls on his back, both benches behind him topple (in the shot from the ceiling of the church). You can't see that the benches are connected and even if they were, the bench he doesn't actually touch wouldn't topple. (00:07:35)
Deliberate mistake: When King Willie is confronted by the Predator in the alley the Predator approaches him cloaked stepping through the puddle of water. You can see his footsteps causing the water to splash up. However, you can see the water splash up and go through his foot. The Predator is only cloaked, not intangible so the water should have splashed upon his foot, not go through. Water against his foot would be visible too, even though he is cloaked. (00:47:45)
Deliberate mistake: When the heads of the families assemble in the Palazzo Azzuro in Atlantic City and get attacked from a helicopter the rotors make the glasses on the table shake and the piles of fruit in the bowls collapse. As the Palazzo looks like quite a solid building this effect is a bit exaggerated. (00:59:35)
Deliberate mistake: It would be impossible for anyone to push up on a casket lid six feet underground and make the lid move much less crack enough to get their whole body through, the dirt would fill the box and trap the occupant.
Deliberate mistake: When Steven Seagal and Kelly LeBrock are in the jeep, being chased through some fields by the cops, some of the shots of the jeep are flipped. Note the bullet holes on the windshield switch sides, as does the driver/steering wheel, the windshield wipers and the front license plate. As an aside, also note the numbers/letters on the license plate that have been altered via CG in the flipped shots.
Deliberate mistake: Morse code takes a lot longer to type out than the captain of the Dallas seems to need. Likely "compressed" because otherwise the process would be quite dull, but still.
Deliberate mistake: Kathy Bates gives James Caan his Noveril a number of times, but one particular time Kathy gives him his Noveril and leaves the room. When the camera shows James Caan holding the capsules between his thumbs and forefingers, it is apparent that they are not James Caan's hands in this shot.
Deliberate mistake: When Andy opens the tap to the liquid plastic it is that some of the liquid squirts on his hand. That would hurt and stain, but Andy doesn't seem to care... (01:14:35)
Deliberate mistake: The same shot of the railway station concourse is used when Graham and George are heading to work, and also when George commits suicide. The giveaway is that several people are seen in the same position. (00:05:00 - 01:20:30)
Deliberate mistake: When Robocain tries to use his chaingun on Robocop and it isn't armed, he snatches the remote unit from the OCP psychiatrist. If you look carefully, the remote unit changes from real to animated as soon as he grabs it.
Deliberate mistake: While Cohagen is on Mars, he calls Richter and chides him for trying to kill Quade. Richter is in a car on Earth, yet they're having a real-time conversation, which is impossible because of the distance. [While this is true, a movie with 4 to 21 minute pauses between lines would take rather a long time].
Deliberate mistake: When the people come into the club looking for money off the owner a fight breaks out between the Krays and the people the Krays stick a sword through the gang leaders hand. But it quite obviously goes through the gap in his fingers. (00:35:10)
Deliberate mistake: In the whole of the 'Psycho' series, there has never been a closet door next to the dress cabinet in Mother's room, but for this movie there is suddenly a closet.
Deliberate mistake: After Ryan and Michelle finish changing the flat tire and are surprised by Leatherface, he chases Ryan around the back of the car and smashes the windshield. At the moment the camera is in the backseat shooting out, we see the chainsaw with the chain popped off and hanging. My best guess is that it was done intentionally (for safety reasons) because the saw was close to Ryan. The crew must've been too lazy to completely remove the chain and just popped it off the track instead. (00:25:25)