Revealing mistake: When the stewardess asks April to sign her copy of the book entitled "How to Survive a Sharknado and Other Unnatural Disasters..." it's a thin book, and in the closeup as April autographs the page we can read the text and it's actually one of the versions of the "Samsung Galaxy Tab...For Dummies" book, not April's book. Also notice when Kelly Ripa shows April's book to the audience, it's now at least 4x as thick.
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: When Tom and Anna were jogging on a dirt path, the woman going in the opposite direction who passes them on the right would be walking straight into the kids (and woman) who were running past them on the left - but the woman on the right disappeared behind Tom's back where the collision would have occurred if she were really there. [Use of a green screen]. (00:29:25)
Revealing mistake: The room Jim and Neville are in is equipped with a double interior wrought iron security gate that appears to be automated, but it does not actually function like a motion-sensored one typically would. The double doors are open before Neville's bookkeeper exits, and where Neville is standing might explain why both sides of the gate are open and stay open until the bookkeeper re-enters. However, they close behind the bookkeeper (and at different rates), even though Neville has not moved. (00:09:26)
Revealing mistake: About seven minutes in, during the scene where we see Cooper helping the Nerd as a cameraman, you can tell that Cooper has been added to the scene using green-screen effects, as the actor was unavailable to shoot at the location. The lighting on Cooper doesn't quite match the lighting of the scene, and you can see a slight "blur/feathering effect" around him where the greenscreen background was removed.
Revealing mistake: At the end the sides of the grave (which Jack just had dug by spade) are too perfect. Only an excavator could get such neat sides.
Revealing mistake: When the camera pans across John's family sitting on a pew, there is a few to several inches between each body. The almost-still frame closeup view from John's end shows the bodies cramming/overlapping and the first four are blurring. (00:11:03)
Revealing mistake: When the tanks are firing on the building near the end, some of the shots of shells hitting the building are reused. (01:35:00)
Revealing mistake: Late on in the film; Arnie and the female officer kick in the door to one of his teams house. Unfortunately Arnie is in his 70s now and not as agile as he used to be, the door was open and simply pushed hard. Look at the door, it has no damage and neither does the frame. Also, the door barely opens past a hard push. As tactically trained operatives they would not have pushed the door if it was ajar either, they would have opened it slowly to avoid startling anyone inside and warning them.
Revealing mistake: When James is getting on the St. Charles street car at Carondelet it's raining, but on the north side of Canal St, people are walking in shorts and with no umbrellas.
Revealing mistake: It is obvious that the actor, Ellar Coltrane, is watching and waiting for the cue for "Mason" to start drinking from his can of beer at the pool hall. (02:03:44)
Revealing mistake: Crawling through a fire cave you can see propane bottles in the background several times.
Revealing mistake: In the beginning of the storm, a trashcan is blown down the street, by the wind. Most of the leaves, lying in the road, are not moving though. (01:28:05)
Revealing mistake: In the scene were Viago is showing the locket that his girlfriend, Katherine, gave him, he puts it on, and since it's silver, it starts to burn his skin. The smoke from his burning flesh is coming from something on the table in front of him, not from inside his shirt.
Revealing mistake: When Millie is being carried away, her head remains completely upright as though under her own control. If she was dead her head would hang back.