Continuity mistake: A box appears in front of Harry's feet when he is unconscious in the alley.
Continuity mistake: In the hospital, the wide shots show Harry's head close to the edge of the pillow. In the close shots it is farther away.
Continuity mistake: Flint raises his right arm to protect himself against the huge flood of water coming. His movement is not continuous in the two different angles that follow.
Continuity mistake: When the black cop hands Flint's file to the Captain, the wide shot shows no one walking nearby. In the immediate close-up, a woman passes by really close to them.
Continuity mistake: When Edward arrives to photograph Gwen's agony, he and the Captain are alone, with two firemen running several meters behind them. In the next shot, Edward is standing with two cops right behind.
Continuity mistake: When the cop is about to climb on the truck, there's a grey car behind a yellow cab on the lane next to him. In the wide angle the grey car is nowhere to be seen.
Continuity mistake: Peter watches the promo on the street and turns around to look at the kids. When the angle changes he is turning again.
Other mistake: Considering Peter's strength and anger plus power of the symbiote, there is no way that Mary Jane would be completely unscathed after he accidentally hit her.
Continuity mistake: When the office floor is collapsing, an employee with yellow folders magically appears next to the model in pink in the close shot and disappears on the wider ones.
Continuity mistake: When Peter is dancing with Gwen, a chubby guy behind is snapping his fingers or waving heartily. The following shots of his movements, couple frames later, show him in totally different positions.
Continuity mistake: When Peter is visiting Harry in the hospital you can see behind Peter an admissions desk with a computer, files etc., yet when Peter and MJ leave Harry at the request of the nurse, the admissions desk has vanished and has now turned into just a plain long corridor with rooms to other patients.
Continuity mistake: When the Captain arrives at the crane scene, he parks on the right side of the street, next to the curb. When he looks at the chaos, the POV and his position show him on the left curb.
Continuity mistake: When Edward enters JK's office the secretary stands up and picks up the phone. In the next angle the phone is gone.
Continuity mistake: In JK's office, the first three bottles of pills are equidistant from each other. From the back, two of them are very close together.
Continuity mistake: In the bell tower, Eddie throws his jacket to the right, but it appears on the left side a second later.
Continuity mistake: At the very beginning of the film when we first see Peter, 4 kids stand beside him and watch Spider-man on the big screen. Watch closely when they walk away, the little girl walks off first followed by the 3 boys, yet in the following shot the girl is at the very back with the 3 boys leading the way.
Continuity mistake: When Venom dies, from the front shot Peter takes his hand away from his face. From the immediate back shot he still has it placed there.
Continuity mistake: During the Peter/Harry fight at the beginning of the film, when Peter retrieves the ring from the air and then falls onto a rooftop, if you watch closely the large air vent moves from being from Peter's right out of shot, and when the shot changes to him starting to run, the air vent is now much further behind him.
Continuity mistake: In the scene where Spider-Man is receiving the key to the city just after he kisses Gwen, we see MJ walk away and Harry standing next to her asking if she's okay, in this shot we can see her handbag has slid down her arm and is resting on her forearm, yet when the sandstorm breezes through, the angle cuts to the back of MJ and Harry and in this shot we can see the handbag is still on her shoulder.
Continuity mistake: When Peter is blinded by the metal pen in class, he covers his eye and forehead. A frame later, the new angle shows his hand away from his face, covering part of the eye and cheek.
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