Corrected entry: When Professor Snape caught Harry missing the curfew, Professor Lupin came to intervene and save Harry from being punished. Lupin also took a parchment, the Marauder's Map, before Snape could confiscate it and asked Harry to come to his office. In his office Lupin mentioned to Harry that the map was a weapon for Sirius Black but he never asked Harry what is hidden inside the parchment nor did Harry ever mention a word about the map. Obviously Lupin should have had no knowledge about the Marauder's Map if he have never even heard anything about it.
Correction: Lupin was one of the people who MADE the Marauder's Map (he was the "Mooney" in "Mooney, Wormtail, Padfoot and Prongs).
Corrected entry: When Harry and Hermione watched their past selves from the wood, there were some scenes where events happened too fast in second scenario. They see Lupin say "Immobilis" and the Whomping Willow stops moving, then just a few seconds later they see Snape coming. But the first time, Snape arrives in the Shrieking Shack few minutes after Lupin. Also Lupin transforming into a werewolf is too short in the second scenario. Hermione howls a few seconds after he changes, but the first time, Lupin transforms, then he fights with Sirius for about a minute.
Correction: The second time we see all these scenes, i.e. when Harry and Hermione have gone back in time, we aren't seeing them in real time. The director has displayed the scenes differently to the audience, in order to underscore that they are now shown from a different perspective (time-traveling Harry and Hermione's). This was an artistic choice by the filmmaker, not a film mistake.
Corrected entry: In the scene where Snape takes over the Defense against the dark arts class, (about werewolves) when the projector changes slides, on the screen the image moves clockwise at the top. However, when you see the projector, the light enabling a picture to be projected is on the bottom and the slides rotate counter clockwise.
Correction: Many projectors flip the image, showing it on the screen upside down and backward to the film's orientation. This must be one of those projectors.
Corrected entry: In Chamber of Secrets and The Philosopher's Stone, the Fat Lady's portrait is located in a hall near no stairs. In this movie, the portrait is located on the stairs.
Correction: That's a conscious choice by the filmmakers - several things change around between the two/three films due to them having different views on how they want the scenes to look (most prominently the location of Hagrid's hut). But if one is to be pedantic about it; the portrait is a painting. It can easily be taken down and moved to a different location.
Corrected entry: Just after Harry and Hermione rescue Sirius, they proceed to enter the clocktower from the courtyard; however, just after they enter the doorway and disappear, a figure can be seen in the doorway that hovers for a second, then shrinks, and moves to the side.
Correction: As the camera pans upward, we see Hermione, followed by Harry, run through the cathedral-style archway, and once they enter the lit doorway within, first Hermione turns to the right and then Harry turns to the right, so both are gone from view at this point. It is Harry who is the "figure...seen in the doorway" just before he turns to his right.
Corrected entry: In the very beginning, Harry is performing the Lumos spell in his bedroom. He's underage, therefore he should be well aware that he's breaking the secrecy rule and should have been alerted to the Ministry, yet they only take notice of him when he 'blows up' his aunt.
Correction: They only intervene when he blows up his aunt, but that doesn't mean that they didn't notice when he used the Lumos spell. Regardless, the Ministry is shown to have discretion in these matters. Harry gets into trouble for blowing up his aunt because there are Muggles present, thus violating the Statute of Secrecy. The same applies in Order of the Phoenix, when he uses the Patronus charm with Dudley present. A student using a low-level spell with no Muggles present, thus not breaking the secrecy regulations, in a manner that clearly indicates that they're practicing, is not going to worry the Ministry.
Corrected entry: Hermione says that Harry wouldn't want to run into himself in the past, that he'll go mad. There have most likely been many instances when something like that would happen, a polyjuice user encountering the sample, for instance. It would probably cause confusion, but it's very unlikely that someone would go insane as a result.
Correction: She meant Harry's past self, who doesn't yet know about time-travel, would. At any rate, it was a figure of speech. Not that he'd just start drooling in his Cheerios with an Aluminum foil hat on his head at the mere sight of himself. Just that his past self's reaction could be dangerous.
Corrected entry: When Harry is going to his room at the Leaky Cauldron, after talking to Fudge, we see Tom walk out of the room with nothing in his hands. In the next shot, he is carrying Harry's books.
Correction: When Tom pushes Harry's chair back and pulls the boy by his shirt, we see the stack of books in the crook of Tom's right arm, just before he walks out the doorway.
Corrected entry: When Peter Pettigrew is seen on the Marauder's Map, his dot's footprints are displayed as that of a human's even though he is in his rat form. However, during the credits Sirius' dot is shown changing from human footprints to dog pawprints and back again. Either Peter's prints should've shown up as rat prints or Sirius' should have consistently been shown as human prints.
Correction: That was just something cute they did for the credits, it isn't meant to be taken as film canon. The Marauder's Map shows what is truly there; Peter Pettigrew is a human whatever shape he may take, so his footprints appear on the map as a human's.
Corrected entry: Platform Nine and Three Quarters is supposed to be a secret platform that only magical people can access. However when Harry, Ron and Hermione have boarded the train and are looking for a cabin we can see out of the window a GNER (Great North-Eastern Railway) train visible on the next platform. The train is most noticeable for its blue colour with a single red stripe running the length of the train.
Correction: The Hogwarts Express is very much the same as the Knight Bus that Harry takes to the Leaky Cauldron, in the sense that muggles cannot see it, even when in the same vicinity as other cars. The same principle applies for the train sitting on the platform at the station next to the real trains.
Corrected entry: When the Dementors are boarding the train, everything starts to go cold, so much so that the water on the windows starts to freeze, and even more noticeably the water in the bottle completely freezes. Once the Dementors have gone, the windows are completely free from ice and the water in the bottle has melted again. This is not possible in the short space of time that passed.
Correction: Neither water nor windows can freeze that fast either. Dementors are magic creatures, and have magical effects on their surroundings.
Corrected entry: When the Hogwarts Express stops and Ron turns to look out the window, Hermione says "Ouch Ron, that was my foot". However, in the next shot, Ron's feet are nowhere near Hermione's. He would have had to have been leaning in order to reach her foot, and he's sitting up pretty straight, too fast for it to change in one shot.
Correction: It's pretty dark and Hermione might have mistaken a big shape for Ron.
Corrected entry: When the entire school is banqueting after their arrival, D. Malfoy says: "Potter. Is it true you fainted. I mean you actually fainted?" In the book, he found out because Neville was in the compartment as well, and he told "nearly everyone." But, in the film, only Harry, Hermione, Ron, and Professor Lupin are in the compartment. The three friends wouldn't have told them, and a schoolteacher doesn't go around telling such things to students. So, as Harry himself asked, how did Malfoy find out?
Correction: There are large windows on the compartment facing the hallway, which showed considerable traffic previously and in the other movies because the snack cart was located farther up the train. It is reasonable that someone saw what had happened during the time that Harry was unconscious or was alerted to the scene by Harry's screams, that Ron discussed.
Corrected entry: In the scene where Hermione is about to punch Malfoy, the wand Hermione sticks at him is in her right hand. It cuts to the next scene, and Hermione punches Draco with her right hand. You never see her wand switch hands in between.
Correction: Hermione would have plenty of time (off-camera) to switch hands.