Continuity mistake: In the scene where Marco falls into the sand molecular chamber, if you watch closely when Marco looks up in one shot you can see he is wearing a chain around his neck, yet in the following shot when the lights come on the chain has gone, and then the shot changes to the scientists, then back to Marco where the chain has reappeared on his neck. (00:23:05)
Continuity mistake: When the sacks of money are handed over to the guard at the back of the armored truck, note the license plate number begins with "13022" but then it changes to "48321" during the rest of the scene. (00:49:20)
Continuity mistake: Reporter Jennifer Dugan's fringe swaps from right to left between the moment when she is reporting about Sandman, Venom and Spidey's fight and the moment when she appears on the news one frame later. (01:53:25)
Continuity mistake: During Sandman's attempted heist of the armored truck, he punches Spider-Man through the side of the truck, and the damage to the armored wall significantly changes in the following shots.
Continuity mistake: The stickers on the board in J.J. office change from when Peter first goes in and when Eddie and Peter leave.
Continuity mistake: When Peter meets Mary Jane backstage after her first performance, her hands continue to move on and off of Peter's shoulders between shots.
Continuity mistake: During the scene on the bridge where MJ breaks up with Peter, MJ's hair is tied behind her head with a few wisps hanging down and her ears visible whenever she is shown from behind. However, whenever MJ is shown in her own close-up during the same conversation, her hair is down loosely and her ears are completely covered up.
Continuity mistake: During the final fight scene, Spiderman is talking to Mary Jane while Harry is flying around. There is a shot of the Sandman about to clap his hands together around Harry. As the scene cuts to Spiderman taking off to save Harry and cuts back, Sandman's hands are much farther apart than they were before the cut.
Continuity mistake: During the battle among Venom, Sandman and Spider-Man, we see a news reporter with an English accent. She is narrating the fight, standing to the immediate right of her cameraman, who is pointing his camera skyward, at the fight. The reporter begins voicing her concern over the outcome. There is a cut to a TV showing the news report, where we see her finish her thought. Except we see a head-shot of her, and not the shot of the battle we should be seeing, considering the positioning of the camera.
Continuity mistake: At the police station, Garret places the picture of a criminal on the desk, then Flint's picture on top. Peter takes the top picture and walks away; but in the background 2 photos can be seen laying on the desk.
Continuity mistake: In Harry's hospital scene, in one shot there is a medical device with tubes next to his pillow. In subsequent shots there are tubes only minus the device. In a later scene, when Harry is getting his memory back, his reflection of the hospital scene again has the medical device.
Continuity mistake: When Venom is choking Spider-Man and the Sandman is punching him as a giant, Spider-Man's mask is cut and under his eye that is exposed, there is so little mask that it is about to snap. Later in the same scene, there is a lot more mask there.
Continuity mistake: The aerial view of the slime falling on Eddie shows no door or light coming from behind him. However, in the close shots, there's an open big door behind reflecting a lot of light.
Continuity mistake: There are several scenes in the film where Peter's 'Spider-Man' costume can be seen sticking out from the top of his shirt, both the 'normal' red/blue version and the black symbiote version. The spider chest-emblem is visible in each of these scenes, but the emblem is smaller and much farther up the front of the costume, almost near his neck. Invariably, whenever he switches into full 'Spider-Man' costume, the emblem has reverted to its original much-larger size and is much farther down the front of his chest, level with his pecs.
Continuity mistake: In the scene where Gwen sees Peter in the restaurant she places one hand on his shoulder. The camera cuts to Gwen's face and she has both hands clasped together in the shot. The shot cuts back out and her hand is instantly down on Peter's shoulder. It cuts back to Gwen one more time and both of her hands are back up near her face.
Continuity mistake: In the scene where Peter asks Harry to help rescue M. J. (from Venom and Sandman), a sitting chair appears to the left of the painting of Harry's father in the last shot of Harry. There was no chair in the other shots of this scene. The sitting chair was by that painting for all of the movie except those few shots.
Continuity mistake: At the end of the movie MJ is holding onto Harry's hand with both of her hands. There's a quick cut back to a view from farther away. Peter and Harry are in the same positions, but one of MJ's hands has instantly moved down around Harry's chest.
Continuity mistake: When Mary Jane halts the cab, there's a couple walking behind her, who disappear in the close-up of her opening the door.
Continuity mistake: Down in the sewer, the wad of dollar bills moves away from the puddle between the close and wide angles.
Continuity mistake: Before Harry throws the bomb at Evil Peter, two bombs can be seen together next to the place where he is lying. Half a second later, when Harry picks up one of them, the grenades are apart from each other.
Chosen answer: Answered in the comics: Peter's Spider-Sense tells him if someone is looking when he's about to enter/exit the apartment as Spider-Man.
Captain Defenestrator