The Harry Potter films are full of Adaptation Explanation Extrication. One major reason why the series is so guilty of this is that the book series was still ongoing while the films were being made, so the scriptwriters had no idea what bits might provide pertinent background for future events. Another reason is that, with the books becoming longer and more intricate, it simply left the films with less and less room to fill in certain background details. The first two films are about as close to word for word adaptions as one can get, but things started getting cut in spades with the third.
See also Adaptation-Induced Plot Hole.
- Harry Potter and the Philosopher's Stone:
- Less flagrant than other examples of this in the films, but no mention is made of Smeltings Academy, so Dudley just happens to be wearing a maroon tailcoat, orange knickerbockers, and a straw boater hat
for no apparent reason. However, a deleted scene (restored in the extended edition) shows that he was wearing those clothes because they were his new Smeltings school uniform and was posing for a photograph in them. - In both the book and the film, Harry receives the Cloak of Invisibility on Christmas Day with a mysterious anonymous note telling him, "Your father left this in my possession before he died. It is time it was returned to you. Use it well." At the end of the book when Harry is in the Hospital Wing, Dumbledore reveals that he was the one who gave Harry the cloak. This reveal is left out of the film, and is not brought up again in later films. While a non-reader could still make the guess that it was Dumbledore, the films ultimately leave it ambiguous.
- An arguably important line is left out of the movie. When Prof. Quirrell reveals Snape had saved Harry's life at one point, Harry is confused, saying he thought Snape hated him. Quirrell replies, "Oh, yes, Snape hates you, but that doesn't mean he wants you dead."
- Less flagrant than other examples of this in the films, but no mention is made of Smeltings Academy, so Dudley just happens to be wearing a maroon tailcoat, orange knickerbockers, and a straw boater hat
- Harry Potter and the Chamber of Secrets:
- The first movie clarifies that underage wizards cannot use magic away from school, but as Hagrid points out to Harry, the Dursleys don't know that. The second book rectified this by Harry receiving a warning letter from the Ministry due to Dobby's Hover Charm, which wasn't carried over into the film. This makes it seem odd that the Dursleys would be satisfied with keeping him locked in his bedroom, when as far as they know, he could easily use magic to escape.
- Justin's status as a Muggleborn is never mentioned in the film except by inference and it's never explained how Harry knows who he is. The Extended Cut fixes this by adding back his introduction where he reveals he's Muggleborn to Harry.
- Without the book's explanation that Filch is secretly a Squib — descended from a magical family, but unable to do magic himself — it's left a mystery why his cat, of all things, would be the basilisk's first victim in the movie, nor should he have had an immediate reason to think Harry was responsible. The scene establishing Filch as a Squib was originally filmed, but ended up being cut from the final product.
- Related to the above. In the book, Harry discovers a letter in Filch's office revealing that he is taking Kwikspell courses in a (vain) attempt to learn magic, whereupon an angry Filch kicks Harry out of his office. Soon after, Ron explains to Harry exactly what a Squib is. The extended version of the film has a similar scene where Harry discovers the Kwikspell envelope and hands it to Filch, causing Filch to snatch it away uncomfortably. However, the film never elaborates on it beyond this, leaving both the Kwikspell envelope itself and its relevance to Filch unexplained.
- Harry Potter and the Prisoner of Azkaban:
- The movie adaptation doesn't explain that the Marauders were Remus Lupin, Peter Pettigrew, Sirius Black and James Potter, with their nicknames based on their animal forms. The film implies Sirius and Peter only became Animagi to escape justice, while they actually did so to keep Lupin company during his werewolf transformations. Later films partially rectify this issue by having Peter consistently referred to as Wormtail, and Sirius occasionally by his nickname, Padfoot, remedying the confusion for attentive viewers.
- Moreover, James's ability to transform into a stag isn't mentioned at all, causing Harry's stag Patronus to lack the significance it had in the book. This also makes the connection to the Marauders even more of a stretch, as there's no other reason to tie the "Prongs" nickname to James.
- It's never explained exactly how Sirius supposedly betrayed the Potters to Voldemort, making him indirectly responsible for their murder. The book elaborates that they cast the Fidelius charm, whereby a secret is made in principle unknowable unless the designated steward chooses to reveal it. In this case the Potters went into hiding by making Sirius the secret keeper for their location, which erased all evidence of their existence to everyone else, but Sirius later made Pettigrew the secret keeper in his stead so as to make any attempt by Voldemort to pursue him for this information futile.
- The movie also never explains how Sirius escaped from Azkaban or how he knew where to find Peter once he had. In the book, he caught a glimpse of Peter's Animagus form in a newspaper photo that Cornelius Fudge had on him during a prison visit; this was what gave him enough willpower to assume his Animagus form and attempt an escape, and his less-complex thoughts as a dog kept the dementors from sensing him.
- The convenient appearance of the Knight Bus just after Harry had run away also isn't explained in the movie. The book explains how the bus can be summoned by a stranded witch or wizard raising their wand into the air, much as Harry did against the Grim in both versions.
- In the book, it was explained that the Dementors guarding the school grounds could see through Harry's invisibility cloak, thereby justifying his need of the Marauders' Map in order to sneak into Hogsmeade through a hidden tunnel. Since the movie leaves this fact about the Dementors out, there doesn't seem to be a substantial reason why the cloak alone wouldn't have sufficed, apart from a brief gag where Fred and George catch Harry trying to sneak out with it due to the footprints he's leaving in the snow.
- Harry Potter and the Goblet of Fire:
- At the end of the book, Harry gets his winnings from the Triwizard Tournament, but out of guilt gives them to the Weasley twins to go towards their joke shop. This also tied into a subplot where the twins got swindled due to a bet they made on the Quidditch World Cup. The movie leaves out both of these, making it seem out of place that a family as poor as the Weasleys would be able to turn out the kind of establishment seen in the sixth film all on their own.
- The film also leaves out the scoring for the first Triwizard task, but leaves it in for the second. As a result, non-readers may be confused when Harry is said to be tied for first place at the beginning of the third task, as earlier he was only said to have come in second place. In the books, Harry scored higher than Cedric in the first task, but lower than him in the second, causing them to tie when the two scores were averaged. Presumably this is true in the film as well, but it's not explained.
- During the second task, it's not explained that the people underwater were never in any danger, implying that they could have died by drowning had Harry not saved them.
- Early in the book there's a scene in which Barty Crouch Sr. uses the Prior Incantato spell on Harry's wand, to reveal the last spells made by the wand. Later, when Harry and Voldemort have a duel and Voldy's wand is hit by Harry's attack it starts being affected by this spell, making all the previous spells used by Voldemort show, including creating Wormtail's new hand and, of course, the last few murders he did, between them Harry's parents. All of this is later explained to Harry by Dumbledore. In the movie, though, the early scene with Barty Crouch is never shown, and when Harry and Voldemort have their duel and the latter's wand starts spewing out ghostly images of dead people there's no explanation for it, and people can't assume they're being shown the wand's latest spells because it only shows the dead people and not Wormtail's hand. Later, when Dumbledore is talking to Harry, when he learns about what happened he merely says Priori Incantatem without offering any explanation.
- The circumstances surrounding the death of Barty Crouch, Sr. differ greatly between the book and film. In the book, he shows up half-mad in the woods near Hogwarts (having spent days fighting off the Imperius Curse, as explained later), but disappears when Harry runs to go get help, later revealed to have been murdered by Crouch, Jr. The film changes it so that Crouch appears to see through his son's disguise as Moody, but is found dead in the woods in the very next scene, and then forgotten about soon afterward. There's definitely the implication that Crouch, Jr. killed him, but it isn't directly stated, nor is he confirmed to have known anything about Voldemort's plans to begin with.
- Harry Potter and the Order of the Phoenix:
- The Dementors attacking Harry at the beginning of the book is largely suspected to be thanks to Voldemort commanding them now, only to be revealed that Umbridge sent them — hoping to silence Harry or discredit him further. In the film, Umbridge never confesses to it — though she does look quite guilty when delivering her line about Dumbledore suggesting a Ministry member ordering the attack. Ultimately, the film never directly addresses who sent the Dementors after Harry, leaving it ambiguous whether it was Umbridge as in the book, if Voldemort sent them, or if the Dementors were acting on their own.
- Minor one. Tonks explains in the book that she has a rare ability to change her appearance at will because she's a Metamorphmagus. She doesn't say this in the film, so it's not really explained why she can change her hair and nose.
- There's a scene where Harry and company are rounded up by Draco and his goons in Professor Umbridge's office. In the book, Luna and Ginny cause a ruckus as a distraction in the group's thought-out plan to sneak Harry into the office, and Malfoy takes Neville in for trying to stop him from taking Ginny, but in the movie they outright skip the planning scenes and don't even hint at the girls' involvement. Draco simply brings the three in, says "caught this one [Neville] trying to help the Weasley girl", without an explanation as to why Ginny and Luna were caught.
- Since the previous film omits all the scenes of Hermione and Ron coaching Harry in useful spells for the third Triwizard Tournament task, one could wonder where Harry suddenly learned all this stuff well enough to teach it.
- The details of Percy's defection to the Ministry are limited to a few appearances without dialogue.
- Harry Potter and the Half-Blood Prince:
- Several scenes which explained Voldemort's background are missing, in particular, the scene where Dumbledore explains what the Horcruxes might be, making the nature of the Horcruxes in the subsequent movies seem much more random. In the following films (most notably when Harry searches for Hufflepuff's cup), Harry has a sort of "Horcrux-sense" (presumably from him being a Horcrux himself) that helps him find the unknown Horcruxes. There also isn't a lot of explanation to why Dumbledore knew a Horcrux would be lurking in that cave in the Half-Blood Prince film. Yes, a photo of the very cave is seen in Tom Riddle's childhood, thus why Dumbledore would logically suspect its correct hiding place, but it's easy to miss and the "field trip" is not touched upon.
- The Reveal that Snape is the Half-Blood Prince doesn't include the fact that 'Prince' was his mother's maiden name, making his adoption of the title 'Prince' sentimental rather than ego-driven.
- Harry Potter and the Deathly Hallows:
- The shard of the mirror Harry uses to communicate with Aberforth Dumbledore is a slightly odd example — it was originally given to Harry by Sirius in Order of the Phoenix, in a scene that was left out of that film adaptation, and yet he suddenly has it at the beginning of Deathly Hallows Part 1. Part 2 does explain that Aberforth's mirror was bought from Mundungus Fletcher, who stole it from Sirius's house, as in the book, but there's still no explanation of where Harry's shard came from.
- Remus and Tonks have a blink-and-you-miss-it scene where Tonks is apparently about to announce her pregnancy, but is interrupted. Their relationship is not mentioned again, until a scene late into in Deathly Hallows Part 2 when Harry is aware of their son Teddy's existence, despite it not being established before.
- At the beginning of the film, Snape is shown telling Voldemort the Order of the Phoenix's plans to move Harry from Privet Drive. It's not clear how he got this information, since Snape is obviously no longer a member after killing Dumbledore in the last movie. Likewise, after they are attacked, Lupin speculates that someone in the Order betrayed them and told Voldemort the plan, but this is never followed up on. In the books, the entire plan was actually formulated by Snape (and Dumbledore's portrait) and Snape confunded Mundungus Fletcher into believing he'd come up with it on his own.
- The movies never explain that Sirius willed his house — and by extension Kreacher — to Harry. So there's no explanation in Deathly Hallows Part 1 when Kreacher obeys Harry's every command (despite his clear distaste for Ron and Hermione). This was almost even more inexplicable — the director and screenwriter of Order of the Phoenix had originally intended to cut Kreacher entirely, which would have made the scene even more incomprehensible to people unfamiliar with the books. J.K. Rowling herself intervened during the development of the fifth film, cryptically telling the director and screenwriter — and by extension, readers — that Kreacher would be pivotal to the at-the-time-unreleased seventh book and needed to be kept in the movie.
- The film doesn't explain where Dobby has been all this time since Chamber of Secrets, particularly when he shows up to rescue Harry and co. from Malfoy Manor. The books explained that he started working at Hogwarts after being freed from servitude and gave him various roles of significance in other books, providing the context for why he's still around and how characters like Harry and Aberforth have kept in touch with him.
- A scene explaining the Taboo (Ron mentions hearing about it in the Ministry) was cut from Deathly Hallows Part 1, so it's never explained despite its effects showing up in two plot-critical moments (the book-verbatim Death Eater attack in the café, and a new change to the Lovegood house scene where Xenophilius says Voldemort's name to summon Death Eaters), making them seem like Diabolus ex Machina rather than a jinx.
- The films do explain the connection between Harry's wand and Voldemort's, but leave out Dumbledore's speculation that this connection had extended beyond the wands and to their users, causing Harry's wand to "recognize" Voldemort and defend Harry against him. This can leave movie viewers wondering why Voldemort's attempt to subvert the connection by using Lucius Malfoy's wand instead of his own didn't work.
- Alternatively, it is possible that the filmmakers were attempting to omit this particular plot point altogether, and that Voldemort's failed attempt to kill Harry with Malfoy's wand was merely intended as Foreshadowing of his later failure to use the Elder Wand without also earning its "approval."
- Dumbledore's backstory is broadly hinted at — it's said that his father killed some Muggles, he was once friends with Grindelwald, and he has a brother who isn't very fond of him and a sister who died young — but it's never explained how any of these events tie together. By extension, the film leaves out an explanation of events from The Half-Blood Prince, specifically Dumbledore's reaction to drinking the potion on the journey to recover Slytherin's locket, which Harry recognized in hindsight was due to him reliving the events that led to his sister's death. It was this realization that led to Harry's and Aberforth's faith in Albus being restored, whereas in the movie Harry's wavering trust in him never comes up and Aberforth's is seemingly resolved on its own and without incident. Rectified by the Fantastic Beasts films, which have a younger Dumbledore mention the loss of his sister to another character, and fully explain Ariana’s fate to Newt Scamander in the third film.
- This trope is straddled with a little regarding the Deathly Hallows themselves. In the movie, the Elder Wand and the Resurrection Stone play the same roles they did in the book, but it's never clarified that Harry's Invisibility Cloak is the same one featured in the legend, and that Harry is descended from the third Peverell brother. However, the existence of other Invisibility Cloaks and what sets Harry's apart from them (that being, his cloak never faded or become torn over time, and could not be affected by spells, like the other ones did) was also omitted during the adaptation process of the books. Therefore, there remains the implication that Harry's cloak is the same one from the legend, by virtue of it being the only one seen or mentioned in the films' continuity.
- When Harry's in the "King's Cross" Limbo near the end, Dumbledore explains that there was a Horcrux inside Harry, but he doesn't explain the reason Harry was able to come Back from the Dead at all — that Voldemort using Harry's blood to return in the fourth movie linked them in another way.
- At the end of the book, Harry uses the Elder Wand to repair his original wand, and then presumably either leaves the Elder Wand in the Headmaster's office, or returns it to Dumbledore's grave. In the movie, he simply breaks the wand and throws the pieces off a bridge without repairing his old wand. We don't see him needing to use a wand for the last few minutes of the movie, but it does introduce a Headscratcher.
