Continuity mistake: In the final fight scene between Green Goblin and Spider-Man, the damaged eyepiece over Spider-Man's left eye keeps changing its damage pattern between shots. (01:45:15)
Audio problem: At Norman Osborn's funeral, we see Harry from the side saying to Peter that he is like family, but his face doesn't move when he talks. (01:46:35)
Revealing mistake: During the final fight with the Goblin, Spider-Man is up against the wall and the Goblin goes to stab him with his "quad bladed knife". Spider-Man grabs 2 of the blades and while pushing back you can see all 4 ends of the blades vibrating up and down as if they were made out of rubber. (01:46:55)
Continuity mistake: In the final fight scene, between Spider-Man and Green Goblin, when Spider-Man goes down, suddenly Green Goblin has a kind of weapon on his hand, when in the rest of the fight scene he had nothing. (01:46:55)
Continuity mistake: At the end of the film when we see MJ hugging Peter, in one shot you can see she moves her hand to his neck and close to his ear, yet from the front view, her hand is still on his back. (01:47:20)
Continuity mistake: Near the end of the film the Green Goblin programs his glider to fly at Spider-Man, Spidey jumps out of the way and the glider continues to fly at the Green Goblin. You see a shot of the Green Goblin throwing his hands up next to his head, then a close-up shot of his face where he says "oh" but there are no hands. Then in the next shot from further away his hands are back by his head. (01:49:10)
Continuity mistake: In the final cemetery sequence, Peter and Mary Jane square off for a little heart to heart, with her touching his face tenderly with her black leather gloves. The camera intercuts between front views of both: in hers, her fingers are touching his ear lobe, in his, they are a inch below his ear lobe. In one quick cut of hers, the hand has disappeared completely, then in mid-sentence as they cut back to Peter, it's there again. (01:49:20)
Continuity mistake: In the end sequence between Peter and Mary Jane by Uncle Ben's grave, as the camera switches perspectives, there's a wayward lock of Peter's hair that disappears then reappears in different shots. (01:49:20)
Continuity mistake: The Green Goblin is impaled by the knives on his glider which are shown after they have punched through him and the brick wall, but there is no blood on them. (01:49:50)
Revealing mistake: At the end of the movie, when Peter is placing Dr. Osborn on the couch after he died, as Peter is lowering him, Dr. Osborn's hand changes from being stiff to the hand moving to help being put down. While it's possible it was a natural reflex, I don't think that they are able to help lower themselves with their own hand. Dr. Osborn had been dead for a while anyway. (01:49:50)
Continuity mistake: When MJ kisses Peter in the cemetery, his head is leaning towards his left, and in the next shot, his head is leaning towards his right. (01:53:10)
Factual error: In the museum, Peter is filming in real-time moving biological specimens shot through 'the largest electron microscope on the Eastern seaboard'. You can't film live specimens in an electron microscope. The electron beam only works in a vacuum chamber, in which the specimen - invariably dead - is held. The microscope is identified as a scanning electron microscope, and nobody can fire an electron stream through air. The electrons will collide with gas molecules and scatter, ruining the image.
Continuity mistake: Jameson is sitting in his office when another man bursts through the door. Jameson jumps and turns to look at him twice- first in the wide shot, and again in his closeup.
Continuity mistake: During the fight scene at school, the food that was just on Flash's back disappears.
Continuity mistake: When Peter Parker goes up to his room, about to become Spider-Man, there's a sudden close-up of his face and his fringe looks different.
Continuity mistake: At the end of the film, when they are at Norman Osborn's funeral, just before and after they kiss, Peter's hair keeps changing.
Continuity mistake: When Jameson is talking to his coworker in his office, the other man holds out a paper. From one angle it's in his left hand, and from another angle it's in his right.
Visible crew/equipment: In the school fight scene where Peter beats Flash by punching him and making him collide against a teacher, his tray falls on his face. In that precise moment a camera with a hand on it can be briefly seen on the left side of the screen just a few moments before the shot points downwards.
Revealing mistake: When Norman's assistant is securing his head in place in the machine, you can see a reflection of the green screens in his glasses.
Revealing mistake: When Peter is running on the rooftops, about to take his first giant leap, the aerial shot shows a way too obvious CGI figure.
Chosen answer: "You're trash! You're always gonna be trash, just like her!" - He says this presumably in reference to Mary Jane's mother.