Revealing mistake: In the airplane fight, heavy objects (and people) get sucked out of the door once the cabin is depressurizing, but the cables and the mask tubes on Richard's side stay softly curled and unmoving throughout the scene. (00:06:10)
Revealing mistake: During the plutonium heist, when the truck skids, tire marks from previous takes are visible on the pavement. (00:10:20)
Revealing mistake: Max is having a delusional monologue at the mirror with his imaginary friend. You can notice that the 'gap' between his teeth is represented by a piece of black tape. (00:24:30)
Revealing mistake: When Gwen catches Max's elevator in a rush, she clutches to her chest the same mug that when she went through the door was practically horizontal. Luckily it's one of those movie empty mugs people carry for no reason. There's a similar scene the day after when she carries an empty mug - a different one, incidentally - but that's when she is running away from the security and the mug is supposed to be empty. (00:28:20)
Revealing mistake: Look behind the policeman when he shouts "Sir, get your hands away from the cables, right now." For absolutely no reason the extras (one in particular to the left that was looking in a different direction entirely) remembers to act scared only at the word "get", but the policeman already started shouting before, and sparks have been flying even earlier. (00:52:00)
Revealing mistake: Electro grabs two cables and unleashes the power of dubstep making every billboard and sign fall. In the shot where the billboard for Mamma Mia and Jersey Boys begin to fall, several extras are running towards the camera and there are a few (like a woman to the left, wearing a white pantsuit and a light purple vest) that are laughing as they supposedly escape terrified. (00:58:30)
Revealing mistake: During the "Gone Gone Gone" montage where Peter recaps the parents subplot by plastering his room with various junk about them, he sticks a particular newspaper clipping using tape. The article is an obvious movie prop fake; look at the right of the photo and you can see the paragraph begins with not even a proper sentence; "Cell regeneration, and long time partner and friend to Norman Osborn, went missing", which is the copy and paste from the beginning of the article save the first line. Copy-paste can also easily be spotted from the leftmost to the rightmost column. (01:01:50)
Revealing mistake: Peter, scientific genius, needs to watch Youtube to understand how batteries work (and will need Gwen later to remind him the obvious relation between magnetism and electricity). As he watches the video, we can easily see it's a dummy page; it has 257,529 views, but two subscribers, and with 92 likes and 0 dislikes has still the bar that shows the like/dislike ratio that is about 4/5. The video is stupidly short, just 20 seconds that say nothing about the topic, and when it's 2 seconds from ending it still goes on off camera for about 6 seconds. (01:03:45)
Revealing mistake: Harry Osborn types "Special Projects" (and we see the word taking shape as he types) hitting as the last keys "E", space bar and "G." (01:28:05)
Revealing mistake: As he holds the dead Gwen in his arms, Peter says "Stay with me, stay with me" two times, twice, and then a fifth time "You stay with me." Between the two repetitions, you can see Emma Stone's long eyelashes twitch. (02:02:30)
Answer: Peter could have webbed him up and called the police anonymously.
MasterOfAll
Very likely. However, there was a deleted scene in which Peter, out of anger over Gwen's death, almost beats Harry to death.
Yes. We also see Goblin getting knocked out when all hell breaks loose, and the gears all break apart. Chances are, Peter just webbed him up. (Although, as the other response says, he also got beaten up in a deleted scene.)
TedStixon