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)
Continuity mistake: Peter opens the closet and throws a red jacket on top of his dad's briefcase, then closes the closet. Several shots later, when he opens it again the red jacket is gone. (01:00:05 - 01:01:05)
Continuity mistake: When Peter is home watching the news, he grabs his cell phone and places his thumb on the screen. In the close-up it's away. This swaps back and forth. (01:00:35)
Continuity mistake: Watching the news after his confrontation with Electro, Spiderman picks up from the table the webbing device that got fried. He then throws it back on the table, where meanwhile all the tools shifted around randomly. (01:00:40)
Continuity mistake: Peter is in bed watching the closet with his dad's briefcase inside. He stands-up and his earplug falls out, but a shot later it's back in. (01:01:10)
Continuity mistake: Before Peter googles Roosevelt he drops stuff on the floor. The position of the objects changes drastically between shots. (01:01:20)
Continuity mistake: Peter inputs in Google "What is Roosevelt?" and gets as output for his search "Franklyn Roosevelt + New York" (01:01:25)
Other mistake: When Peter looks up "Roosevelt hotel", the map result shows "Map data ©2013 Google." The movie was shot in 2013 but takes place in 2014. (01:01:30)
Other mistake: We see Peter freshly printing an old news story from CNN; the timestamp on the visible corner says the sheet was printed at 9:18 AM. The scene takes place in the evening. (01:01:45)
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)
Continuity mistake: Harry just found by accident the secret interactive desktop from his father. He drags and drops a menu, but somehow when he checks out the item he highlighted, the menus themselves changed entirely showing stuff like "Max Dillon experiment" that were not there a moment before. (01:03:05)
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)
Continuity mistake: Peter is cooped up in the garage window as he answers the phone after a night of dangerous experiments. First shot and his arms are free, close-up, and he's wrapped in a blanket. (01:05:00)
Continuity mistake: When Gwen nearly falls off her own flats trying to avoid Oscorp's cartoon security, Peter grabs her. She clings to her and her mug hand is against his arm. She says "Hi!" in the next shot and her arm is lowered. (01:09:20)
Visible crew/equipment: We get a good view of the Oscorp corridors, in particular the one outside the closet where Gwen and Peter hide. They kiss and there's a lovely light seeping through the door's window; when they start making out and also quickly when they open the door you can actually see the big spotlight that emits those warm rays. (01:10:49)
Continuity mistake: During the kiss in closet scene, Garfield has his hand on Emma Stone's face abruptly at the cut. Seconds later, when they concur that the kiss was "a bit rushed" they smile at each other with a completely different position - as you can see from the light rays on their faces. (01:10:55)
Other mistake: Peter grabs with his web at super-high speed a mug full of scorching hot liquid that he uses to slapstick his way out of the Oscorp security stooges; somehow the cup clashed against his hand staying perfectly filled and unperturbed, but in the next shot the slightest bump spills coffee everywhere. (01:11:20)
Visible crew/equipment: When the doctor wants to study Electro, a green screen and some other things are reflected in his glasses. (01:14:10)
Audio problem: When Harry listens to the recording of Electro's threats to Dr. Ashley Kafka, the sentence is conveniently edited for brevity, omitting part of the original sentence ("A world without mercy"). (01:15:25 - 01:28:40)
Continuity mistake: Peter comes back home and finds his aunt sitting on his bed staring at his serial killer-like collage. The two start talking, and during the conversation May has several locks of hair on or off the cheek as the two angles alternate. (01:16:45)
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