Deliberate mistake: When the Creeper gets stabbed through the eye with the javelin, it goes through the front of his eye, but when it comes out the other end the eye is facing backward. (00:50:00)
Deliberate mistake: There is one scene in the movie where Heath Ledger reads a Latin sentence in a book. As he is translating the sentence, he goes over the words one by one with his finger. This would never be possible in a Latin sentence, because words in Latin are never in exactly the same order as in English. Words that actually belong together can be placed at opposite ends of a sentence.
Deliberate mistake: When Leota is in the front seat of the automobile, the air bag is still full. Air bags will deploy and then immediately deflate to prevent people (or women in crystal balls) from being trapped. (01:10:45)
Deliberate mistake: When the teacher walks over the floor towards the blackboard, he walks through a lot of blood. However when it cuts, he leaves no traces of blood where he steps.
Deliberate mistake: When Jason throws Freddy to the wall in the burning house, you can see a window on the wall. Now, the distance between the window and the corner of the wall is about five feet. This gives Freddy space enough to hit the wall and not hit the window. However when Jason picks Freddy up you can see the distance has increased to about one feet. It's like they've put in an extra window where there should be a wall instead. (01:14:30)
Deliberate mistake: When Kimberly is being revived, it's obvious that they are using a defibulator. But when Kimberly finally comes to and is covered by a sheet, you can see she has a bra on. This is impossible to have because you need direct contact with the skin in order for it to work. And the machine would start the heart working if it was lower on her chest.
Deliberate mistake: When Kyle goes through the windshield, the windshield shatters like tempered glass. Windshields at the time were made of laminated glass.