The Wizard of Oz famously combined the roles of the two Good Witches (of the North and the South), creating the plot hole where Glinda doesn't tell Dorothy what the slippers do on their first meeting, which would have saved her a lot of trouble. Originally the Good Witch of the North (not Glinda) gave her the shoes, but only Glinda knew they could bring her home. In the film, Glinda defends her withholding of this crucial information by explaining"She wouldn't have believed me!" despite the fact that, being in a magical land with talking trees and animals, Dorothy would have been willing to try anything.
The death of the Wicked Witch of the West was also brought about by one of these. In the book, she'd made Dorothy a slave in her castle while she thought up a way to get the silver shoes from her - the bucket of water was present simply for Dorothy to clean the floors with, and she doused the Witch with it in a fit of rage at having one of the shoes stolen. In the film, the water comes completely out of nowhere when Dorothy uses it, and it makes the Witch look foolish for choosing to set the Scarecrow on fire when her greatest weakness was right nearby to put it out.
Inverted. In the original graphic novel, the disaster that allowed Norsefire to come to power was a nuclear war between the US and USSR in the 60's, and that nuclear fallout caused Britain to be shut off from the rest of the world and most of their food supply to become irradiated. Of course, this raises the question of why the fallout didn't kill everyone in Britain as well, since they're fairly close (as far as radiation is concerned) to the major population centers of Russia. The film fixed this, however, by changing the nuclear war to a simple collapse of many of the world's governments, and a massive plague secretly created by Norsefire.
But played straight in having the government's supercomputer Fate cut out of the movie; V having completely subverted the computer that controlled everything for Norsefire was a major plot point. Without it, his ability to never show up on any of Norsefire's omnipresent surveillance becomes strangely inexplicable.
On Her Majesty's Secret Service is one of the more faithful adaptations of a James Bond novel to film—which, ironically, leads to problems. In the previous novels, Bond had never met Ernst Stavro Blofeld directly, so naturally they did not recognize each other on sight in the OHMSS book. But in the previous Bond movie, Bond and Blofeld had met face-to-face. However, they still do not recognize each other in the OHMSS movie, because they didn't recognize each other in the book! The fan theory is that Bond's plastic surgery to appear more Japanese in the movie You Only Live Twice meant Blofeld didn't recognise him.
Additionally, the films made SPECTRE the antagonist of all but one of the previous Connery films, whereas in the novels they'd only previously been in Thunderball. They even instigated a revenge plot against Bond in From Russia with Love. This makes it even more unlikely that Blofeld had never seen a picture of Bond.
The reboot Blofeld is also at the center of one of these. In the novels, it was explained that Blofeld was Polish economics, politics and engineering major who set up an intelligence service to sell info to both sides of World War II before using his resources and connections to found Spectre. The original film series never explained anything about Blofeld, but there was nothing that contradicted his status as the founder and head of the greatest criminal organization in history. In 2016's Spectre, however, due to the Adaptation Origin Connection of Bond and Blofeld being brothers in law, Franz Obrenhauser/Blofeld was a son of a mountain climber, who murdered his father and faked his own death at a very young age, and would presumably have to start his life from scratch, making his later position as the founder of Spectre a credibility stretching case of From Nobody to Nightmare.
In the book of Sleeping with the Enemy the heroine has to live on oatmeal and beans for months after escaping her abusive husband. The film instead has Laura inexplicably affording a large and spacious house, complete with luxuries like brand name goods. Despite having only a part-time library job before her escape and not working for ages after she does settle into town.
The movies leave numerous questions about Aragorn to people who haven't read the books. If everyone knows him to be the rightful heir of Isildur and King of Gondor, why isn't he already? Why is Aragorn a 'Ranger from the North' if his homeland is Gondor? In the book, Aragorn's ancestry is not nearly so well known, and he has to go to considerable lengths to prove he's the rightful heir to the throne, though even the book left most of this backstory to the appendices.
Frodo ends up face to eye with Sauron when he just puts on the Ring in Bree — a very dramatic and special-effecty scene that's totally absent from the book. If Sauron is capable of linking his mind to the Ring so strongly, even if that's only when it is worn, that leaves questions about why he has no idea where it's moving and being used later on. Also related to the next point.
Near the end of the second film, Frodo clearly displays to one of the Ringwraiths at Osgiliath that he has the Ring. So in the third film, why is Sauron using all his forces to attack Minas Tirith rather than looking for Frodo? In the books, the scene at Osgiliath never happens; Sauron is never totally certain of who exactly has the Ring, but his hunch is Aragorn. This also explains why Sauron's forces fight the Armies of Men outside the Black Gate, whereas in the film Sauron seems to be doing out of a need to defend his reputation rather than any material incentive.
Additionally, in the book it's explicitly stated by Gandalf that Sauron would never consider the possibility that someone might try to destroy the Ring - being a power-obsessed villain, he assumes others would want the Ring for self-interested reasons so they can overthrow him and take his place - which explains why Mount Doom is relatively unguarded, as Sauron wouldn't expect anyone to go there.
In the Return of the King movie, Aragorn, Legolas and Gimli somehow sail a ship up the Anduin to Minas Tirith all by themselves — never mind that none of them have ever sailed a ship before (lampshaded in DM of the Rings), and they'd need a larger crew anyway. Also, somehow the entire ghost army fits on that one ship while the rest are left behind. In the book, they also had thirty-something Rangers with them, plus thousands of soldiers from Lebennin who were free to come to Minas Tirith as reinforcements after the ghosts took care of the Corsairs of Umbar.
People who only saw the films frequently ask why Elrond didnt simply take the Ring from Isildur and destroy it himself? The reason is that the whole DESTROY IT scene just plain doesnt happen in the books. No one knew at the time what the One Ring really was, nor that it was keeping Sauron alive. Isildur takes it as a Battle Trophy and nobody has any reason to object to him doing so, Elrond included.
And of course, overlapping with Adaptation Explanation Extrication, the Eagles. Everybody loves to ask why they dont just ride the Eagles into Mordor like its some huge plot hole, but the movie simply fails to explain the reasons why; the Eagles are ridiculously conspicuous when the plan is to sneak into Mordor, Sauron has tons of archers and fliers that negate the advantage of flying in, and the Eagles dont answer to mortalkind, they get their marching orders from Eru. The movies also make the Eagles seem a lot more powerful then they really are; in the books, its not just a few of them that swoop in at the end and turn the tide, its the assembled armies of their entire race.
In Infernal Affairs, only Superintendent Wong knows the identity of the undercover cop. When he's murdered, the cop has no one in the police department to turn to. In The Departed, both Captain Queenan and his assistant Sergeant Dignam know who the undercover cop is. When Queenan is murdered, the cop acts like he has no one to turn to, but Dignam is simply away on suspension. Why no one bothers to look him up is never explained. Dignam's sudden reappearance at the end is treated as a surprise, but fans of the original would be waiting for that dangling thread to resolve for half the film.
In Transformers comics, transformers with the ability to transform into biological animals (including humans) are known as "Pretenders", who are fitted with special external armor shells so that they can do this when normal bots can't. In Transformers: Revenge of the Fallen however, the decepticon "Alice"'s ability to disguise herself as Sam's classmate seems to come out of nowhere, especially considering the audience was explicitly shown how both mini-cons and normal bots scan their Alt-mode's in the first film, and there is nothing to indicate they can do this on anything non-mechanical.
Overlapping with Adaptation Explanation Extrication, the Earth Kingdom prison camp. In the series, the Earth Kingdom prisoners are trapped on a rig out at sea, and need Katara's help because they have no obvious earth to bend. In the film, the Earth Kingdom prisoners are in a garden-variety landbound prison camp, and need Aang's help because it apparently just hasn't occurred to them that the ground here also counts as earth. While both versions explain that the Earthbenders had their spirits broken and no longer wanted any trouble, the film fails to give a reason for how they lost their spirit, as they always had access to their greatest weapon while their animated counterparts were handicapped.
The film adds the idea that Firebenders can only manipulate pre-existing sources of fire, which raises the question of why all other bending types (or really, anyone with a bucket of dirt or water) aren't able to easily disarm them by simply putting out their fire before or during a fight.
In the show, Aang runs away because he's a twelve-year-old kid who's understandably terrified of having to take the responsibility of saving the world. For whatever reason, the movie changed it to him running away because he was told the Avatar could never have a family. First of all the show very early on established that a previous Avatar, Kyoshi, had a daughter. When they go to Kyoshi Island, they meet meet a girl named after her daughter Koko. Second of all , this would have had huge consequences had they finished the series. Zuko's whole redemption arc hinges on him finding out that his great-grandfather was the previous Avatar, Roku.
In Before I Go To Sleep, it is stated that Mike abducted Christine four months earlier, and since then has taken advantage of her amnesia to pretend to be her ex-husband Ben. In the book, the real Ben (who despite their divorce, still deeply cares for Christine) has not been aware of this because he has been working abroad for several months. The film, however, makes no reference to Ben having been away, but maintains the situation of him not having been in contact with Christine for a long time.
In the book, Christine's friend Claire does not realise and tell Christine that Mike is not Ben due to having been out of contact with Ben for years; she hadn't spoken to him to realise something was wrong. In the film, Claire is easily able to contact Ben, and their lack of contact is instead explained purely out of Claire's embarrassment about her affair with Ben.
The book makes it very clear that Mike is psychotic, which explains the considerable flaws in his efforts at deceiving Christine. The film does not really follow this portrayal of Mike, which leaves the view wondering why his actions are so obviously irrational and badly thought out.
The short story turned short film Paul's Case has an example of this, although it's not so much a plot hole as a moment of characterization kept in when it didn't fit with the other changes. In the original story, Paul is portrayed in a way that makes it easy to assume he has mental problems. In the film he's turned much more sympathetic, and is shown to be a victim of circumstances, yet the film keeps in a scene where Paul creepily fantasizes about his father shooting him when he crawls through his basement window.
Reffering to Prince Caspian: In the book, the kids change back into their old clothes before heading home. In the film, their clothes automatically appear on them, making you wonder how Edmund lost his flashlight.
In the film of The Voyage of the Dawn Treader, a search for seven swords is superimposed over the novel's search for seven missing Telmarine lords. The claim that at least one of these swords was given to Caspian's father by Aslan is an Adaptation-Induced Plot Hole: Aslan hadn't been seen in Narnia for centuries prior to the events of Prince Caspian, and as a Telmarine, Caspian's dad would've been brought up to believe "Aslan" was either a myth or a monstrous lion-demon, not a benefactor.
The same film otherwise narrowly avoids another Plot Hole. On the Dufflepuds' island, Lucy gets kidnapped because only a girl can read the spell to break the enchantment. The film adds another girl, Gael, to the cast. However the Plot Hole is avoided when one of the Dufflepuds notes that Gael is also a girl — but they decide to kidnap Lucy because she has a book next to her, indicating she knows how to read.
In Flowers in the Attic after the husband dies, Corrine has to go back to her rich family and hope for an inheritance or else her children will have no money. The book is set in the 1950s but the film takes place in the 80s (when it was made). Corrine not attempting to work or not having a pre-existing job already is odd since there were less housewives that stayed exclusively at home in the 80s than there were in the 50s. Another one relates to the Age Lift. Chris and Cathy are fourteen and twelve respectively in the book but the movie ages them up to at least sixteen or seventeen. One wonders why they didn't try to find jobs either. Also as they're older, them being afraid of their grandmother is a little less believable - Chris would easily be able to overpower her.
The movie moves Dwight's "Most people think Marv is crazy" monologue from A Dame to Kill For to The Hard Goodbye. This works fine in a standalone movie, but in the comics the chronology of that night is very well fleshed out. It's revealed that while Marv was drinking at Kadie's after Goldie's murder, two cops were questioning Shellie about Dwight's whereabouts. At that point in the story Dwight is recovering from events in his own story, so he couldn't be anywhere near Kadie's that night. Furthermore, he underwent plastic surgery which gave Dwight his appearance in the movie but that only happened months after the events of The Hard Goodbye, at which point Marv was on Death Row. Since Sin City 2 is slated to use A Dame to Kill For as its lead story they'll have to break from their own continuity or alter the timeline and make the entirety of Dame to Kill For take place before Hard Goodbye.
There's also The Salesman, the assassin from "The Customer is Always Right," who later becomes The Colonel, the Big Bad of Hell and Back. Since The Colonel is dead by Boom, Headshot! (and quite deservedly so) at the end of Hell and Back and the events of The Big Fat Kill take place after that story (Manute shows up alive in the former and is killed in the latter), the Salesman doing to Becky what he did to his "customer" in the other story at the very end of the film adaptation can't exactly happen in Sin City canon unless someone else is the Colonel in the film adaptation of Hell and Back.
In the original Total Recall (1990), there was a perfectly legitimate explanation why Hauser had to have his memory erased and take on the Quaid persona: it was because Quato, the leader of the resistance, was a mutant who could read minds, and could therefore detect an undercover spy easily. But in the remake, the leader is just a normal guy without any mind-reading abilities, thus eliminating the need to erase his memory, and making the whole premise of the film rather faulty.
The movie gives a rather weak explanation as to why the Comedian was killed. In the comic it's laid out that it's because he discovered the secret island where Veidt/Ozymandias was conducting genetic experiments allowing for the creation of the giant monster in the climax, but since this part is removed from the film and the ending is changed, it doesn't appear. Rather, the reason given is simply that he discovered Veidt/Ozymandias's plan after being ordered by the government to investigate him, and that's all the explanation we get.
In both the movie and the book, Ozymandias plans to avert a coming war between the United States and the Soviet Union by orchestrating a horrific massacre and blaming it on a non-human outsider, giving the two countries a common enemy to unite against. In the book, he does this by attacking New York with a genetically engineered monster to fool the people of the world into believing that Earth has been invaded by aliens. In the movie, he destroys the world's major cities with a series of energy blasts, and stages them to look like Doctor Manhattan has turned against humanity. The problem is that everyone on Earth knows that Doctor Manhattan is an American citizen who's been a loyal operative of the US military for decades, making it a strong possibility that the rest of the world would hold America responsible for the massacres and be reluctant to join with them.
While the original Battlefield Earth novel isn't exactly regarded as a masterpiece of plotting, the film still introduces various plot holes and problems of its own. Perhaps the most glaring is that the Psychlos somehow missed Fort Knox altogether in the film, whereas in the novel it was one of the first locations they hit. In the novel, the rebels acquire gold from an armored car stocked with bricks. The Psychlo sensors didn't notice the gold 1,000 years prior due to the car's frame blocking the scan. And they overlooked it while literally pulling gold fillings out of people's teeth because they assumed it was a military vehicle.
In the 2012 adaptation of Les Miserables, there are several minor ones that crop up.
In the "Who Am I" number, Valjean simply tells the judge who he is to clear the falsely-accused man's name, providing no more evidence than saying that Javert will recognize him (and given that Javert just spent the last scene saying he now believes that Valjean is not the convict he was looking for, it comes across as Javert having rather bad judgement). In the musical, the script specifies that Valjean proves his identity by showing the tattoo of "24601" branded on his chest.
Another takes place when Thenardier and his gang try to rob Valjean's house. In the play, after Eponine gets rid of them, Cosette pretends she saw three mysterious men lurking outside which caused her to scream, thus causing Valjean to think Javert has found him. In the movie, Cosette has already gone to bed and thus Valjean only hears Eponine screaming and... somehow comes to the conclusion that this means that Javert is nearby.
Eponine still crossdresses in this version, but for unclear reasons as there are women openly staying on the barricades.
In City of Bones, Simon was abducted by vampires because he'd been turned into a rat, and they mistook him for one of them. In The Mortal Instruments: City of Bones, they took him as a hostage because they wanted the Mortal Cup. The movie failed to give us any possible use Vampires could have for the Cup.
Full Circle completely leaves out the connection between its main character and antagonist, which was detailed in the original book.
Dawn of the Dead (1978) was reworked into the very different film Zombi for European audiences, with a faster pace than the American version at the cost of a new plot hole. Originally, Roger and Peter succeed at their first round of barricading the mall doors with trucks, causing Roger to start celebrating while they're getting more trucks, get too cocky, and then get bitten by a zombie. Zombi skips over the first part so Roger's careless behavior comes out of nowhere before they've accomplished anything and is completely out of character.
Minor one in Into the Woods. Rapunzel is actually the Baker's long lost sister, having been taken by the witch when he was a toddler. The Baker never finds this out in the stage show, and it's the same case in the film. The Plot Hole comes from the fact that the Narrator is a separate character in the stage show. For convenience purposes the Baker also serves as the Narrator in the film. And the film ends with the Baker narrating the story to his newborn son. But since he never finds out Rapunzel is his sister, it raises the question of how he knows this in narration.note Though there is a small possibility since Rapunzel survives in the film, that she and the Baker eventually do reconcile some time after the events of the story - as the narration says a lot of things the Baker wasn't witness to, so it could be assumed that the narration we hear is him telling the story much later after getting the rest of the information.
In the play version of Perfect Pie, Marie's reluctance at going swimming is because she's afraid of having a seizure while she's in the water. In the movie adaptation she doesn't have seizures, leaving her fear of going swimming inexplicable.
Virus: Day of Resurrection has a Race Against Time to turn off a nuclear defense network from firing. In both the novel and the film there are two such systems, one in the USA and one in Russia. While the USA mission arrives too late, the novel implies the Soviet team is successful, thus no missiles hit North America. The film makes no such mention of the Soviet team, and total nuclear winter occurs; this making the hero's long walk from Washington to South America nothing sort of an outright miracle as he arrives with nary a hint of radiation poisoning.
Jurassic Park: The first movie slightly modifies the book's ending so that our heroes just leave Isla Nublar behind and fly safely back to civilization, with no mention of the Costa Rican Air Force bombing the island and killing most of the dinosaurs. Despite this, the sequel The Lost World: Jurassic Park features InGen being forced to go to their mostly unsettled breeding ground at Isla Sorna to catch a fresh crop of dinosaurs—with no explanation of why they couldn't just get them from Nublar, which actually has a (mostly) intact infrastructure.
The adaptation of The Foreigner (2017) essentially kept the same backstory from the novel, but moved the main action from the early 1990s to its 2017 release date. Although this works surprisingly well overall, Quan's daughter Fan is still portrayed as a twentysomething student, as she was in the novel. Since Fan was apparently still born in the early 1970s, she should be in her mid-forties at the time the film is set.
There's also the matter of how Quatermain figures out that "M" is Professor James Moriarty in the climax, which is never explained. The movie makes a big deal about Moriartytaking on multiple identities, including "M" and "The Fantom", and the League personally meets with "M" in London before he sends them off on their mission—implying that he isn't someone they would recognize. In the comic book, "M" is just Moriarty's callsign in British Intelligence, and he stays hidden behind the scenes for most of the story before choosing to reveal himself.
Carnosaur : One of the few scenes lifted from the book to the first film was where a Deinonychus fatally mauls two teenagers in a car. In the book it makes sense as it's a man-sized adult animal, attacking at night, and it got to the couple so quickly because a car door was open. In the movie, due to added plot of the Deinonychus inexplicably growing fast across the duration, it's a juvenile about the same size as a small dog, attacks in broad daylight, and all the car doors were shut. Thus a logical sequence because a confusing scene with a killer animal the size and danger level of a schnauzer somehow getting inside a close vehicle to enact a killing spree.
The Avengers (2012) might leave some viewers wondering why Clint Barton and Natasha Romanoff become full-fledged Avengers so easily, since both of them are officially just garden-variety SHIELD agents with only a bit more skill than the average Redshirt, and neither has any superpowers or particular skill with gadgetry. In the comics, they weren't founding members of the Avengers; their spots on the team were occupied by Hank Pym and his girlfriend Janet Van Dyne, who actually did have powers and specialized gadgets. note Hank and Janet were originally going to be in the movie, but were Adapted Out after the planned Ant-Man film (which was going to introduce them) got stuck in Development Hell; director Edgar Wright also got really attached to the project, and requested that the studio leave the characters out of The Avengers so that he could introduce them how he wanted Clint and Natasha didn't join the team until many years down the road, and they didn't start out as SHIELD agents; they were a thief/vigilante and a Russian spy who had many run-ins with the Avengers before undergoing Heel Face Turns, and Tony Stark personally invited them to join the team after they redeemed themselves. And since the Avengers started out as an independent superhero team rather than a special SHIELD task force, there were no questions about why Clint and Natasha were fighting with the Avengers instead of with SHIELD's Redshirt Army.
Suicide Squad has a similar problem to The Avengers (2012) with Badass Normal characters who are iconic to the team being on it without it making in-universe sense. In most comic continuities, the modern Suicide Squad is formed after groups like the Justice League have been established, and is meant to perform covert and often morally ambiguous operations for the US government, which is why they tend to recruit lower-key villains like Deadshot, Captain Boomerang, Harley Quinn, Slipknot, etc. In the DC Extended Universe though, they are formed before any other superhero team, and explicitly exist to serve as a safeguard against superbeings like Superman and Wonder Woman going rogue, making every membership save Enchantress and Diablo questionable at best, especially since the film versions of these villains have nowhere near as much experience as Comic-Book Time has allowed their counterparts to get.
In The Scorch Trials, while travelling across the scorch the Gladers are caught in the middle of a lightning storm, where the lightning appears to be actively chasing them, with several characters getting struck. Its implied, and outright speculated In-Universe by Thomas, that the lighting is being artificially created by WICKED. Maze Runner: The Scorch Trials keeps this scene, but only having Minho being the one struck and removing Thomass theorizing. However, unlike in the book WCKD are no longer in control of the Gladers who have already escaped from them and don't have the level of technology required to artificially make or manipulate a storm like their book counterparts had, making it unclear how apparently naturally occurring lightning is able to chase someone.
Two relatively minor ones crop up in The Martian: Firstly, it's never really explained why Watney never tries to patch up the Ares 3 mission habitat's communications antenna, whereas in the book it's stated that the large microwave radio transceiver dish he needs for direct communications with Mission Control (the large object that was ripped away by the wind and clobbered him in the opening scene of the film) could be anywhere within several kilometres and is probably under two feet of sand anyway. Second, some people have noticed that living on literally nothing but potatoes for months at a time would leave Mark with huge vitamin deficiencies, but the book explicitly mentions that the food the Ares astronauts were supplied with wasn't much better (being shelf-stable for long periods and having a high calorie-to-mass ratio took priority over nutritional balance) so they were also supplied with a huge amount of multivitamin tablets.
Kayano's hair is brown instead of green in the Assassination Classroom live-action movie. This creates a plot hole after The Reveal that she's actually a moderately famous actress. In the manga, nobody recognized her because she dyed her hair green, so it begs the question how nobody in the movie recognized her.