Deliberate mistake: Perhaps to avoid getting an R rating or parental complaints notice how in the operating room massacre none of the doctors appear to bleed nor do Doc Ock's tentacles have blood on them.
Suggested correction: The problem is in both versions of the film, basically all of the deaths either happen off-camera, or are things like people being shocked to death or killed by being tossed around and presumably having their backs/necks broken. Most of the deaths would be bloodless or near-bloodless anyways, and the camera simply doesn't linger on the bodies enough to show any blood. This is also why the tentacles aren't really bloody. Sure, it was probably ratings-related, but it isn't technically a mistake.
Other mistake: During the hospital scene where the robotic arms kill all the operating room staff, we see 4 different camera angles on the last doctor to be killed. All the arms have cameras in them, and show his face screaming at 4 different angles. Yet it should only be 3 as one arm has its claw wrapped around his neck. And it doesn't release from him, as it can be seen still wrapped around his neck by the other 3 cameras in each claw.
Visible crew/equipment: The camera and a boom mic are visible in the police car lights in the scene directly following the first accident with Doc Ock.
Continuity mistake: Right before Spidey stops the train there's a lot of people inside next to him. Then a wide shot later they've vanished only to reappear a shot later.
Continuity mistake: Spidey throws a huge iron minute hand at Ock which destroys an enormous chunk of concrete and makes loads of debris fall downward. However, a shot later there's a view of the street and the train track and not only is the debris gone from the road but the traffic and people act as if nothing had happened.
Continuity mistake: After the car slams the cafe, Peter watches the street with people running around. The reflection on his lenses has nothing to do with what the opposite angle shows.
Continuity mistake: When Peter/Spider-Man has his first web failure and falls on the pipes on the building's roof, he keeps his hands free in one shot and then his right hand is put on his chest in the next.
Revealing mistake: When Peter returns to his old life and walks on the notes of "Raindrops Keep Fallin' on My Head", at a certain point he stumbles and behind him some people look at the camera.
Suggested correction: They are looking in the direction of the camera. It doesn't necessarily mean they are looking at the camera. They could just as well be looking at Peter since he stumbled and fell, which is a pretty normal thing for people to do when someone falls down.
Actually people behind him keeps watching even when Peter restarts to walk normally. I think if they were really watching just him, they would have looked away immediately as he got to his feet.
Continuity mistake: Kids buying fruit suddenly appear behind Peter when he arrives at the pizza place for the first time.
Continuity mistake: Peter back flips off his moped to avoid the car racing at him. There were cop cars and other vehicles behind that car when Peter jumps, but when he lands only one cop car goes past in the lane next to him and the lane he's standing in is then clear of traffic as he talks to some kids.
Continuity mistake: When Peter first sees the burning building, there is a far away shot and you see the guy with dreadlocks run to a woman. Then it cuts back to Peter as he tries to become Spiderman then remembers he can't. Next shot has the same shot, only this time it's a close up of the man with dreadlocks running to the woman.
Continuity mistake: After the bank scene where Spidey saves aunt May from Doc Ock, while they are on the street the sun changes between shots.
Revealing mistake: During the final battle, when Spidey tells Doc Ock "we have to give up the thing we want the most... even our dreams", watch the tentacle behind Doc Ock's head. Right after Spidey says "even our dreams", the three "claws" on the tentacle close, and you can see the tip of the bottom "claw" pass through the tip of one of the other claws, revealing a blunder in the rendering of the digital effect. (This is visible in the DVD release of the theatrical cut of the film. It was corrected in the "2.1" edition, and may have been corrected in the Blu-Ray release, but it's still plainly visible on the original DVD release).
Continuity mistake: During the demonstration of the fusion reaction when Doc Ock is strapping the metal arms to his body, the pins that go in to his spine are shown going in twice from two different angles.
Continuity mistake: In the scene where Peter and Aunt May visit Uncle Ben's grave, Peter's hair is blowing in the wind quite violently in the wide shot but is relatively still in the close up.
Continuity mistake: People behind the pizza guy who stops Peter's motorbike disappear/reappear between shots.
Continuity mistake: During the cafe scene, the spoon under the saucer disappears in the close-up.
Continuity mistake: When Jameson is brought the suit, the position of his secretary's right arm is inconsistent between the front and back angles.
Continuity mistake: The chip on Dr. Ock's nape is 10 centimeters away from his hair. In the close-up it's right next to the hair.
Continuity mistake: When Peter and Mary are talking in the cafe, the same cyclist with a purple shirt and a yellow bag passes by three times repeating all the previous movements.
