Movie Adaptations With Plot Holes That Don't Exist In The Books

Throughout the Harry Potter series, Polyjuice Potion is used to let the drinker take on the appearance of another person. This facilitates a major twist in Harry Potter and the Goblet of Fire, when Hogwarts teacher Mad-Eye Moody (Brendan Gleeson) is revealed to be Barty Crouch Jr., who's been disguised all year to orchestrate the Triwizard Tournament and send Harry to Voldemort's clutches.

Crouch's deception is the only time the Polyjuice Potion works as it does in the books, in that his voice changes as well, rather than being the voice of Crouch's actor (David Tennant) coming out of Moody's body. In every other instance in the films, the person's voice remains unchanged even when their body transforms.

In Harry Potter and the Chamber of Secrets, Harry even acknowledges this plot hole when he disguises himself as Goyle. Even when physically transformed, he still speaks with Daniel Radcliffe's voice, and Ron (who's posing as Crabbe) still speaks as Rupert Grint. The two must affect a deeper tone to their voices to try and fool Malfoy into believing they really are Crabbe and Goyle.

It doesn't make sense why the Polujuice Potion wouldn't change a person's voice since everything about their physiology is supposed to be altered - or why it only happens that way once.

In Greek mythology, Persephone was abducted by Hades and became the Queen of the Underworld. Percy Jackson & the Olympians: The Lightning Thief sticks to this premise but features Persephone's revenge. In the film, Persephone (Rosario Dawson) initially seems to aid Hades (Steve Coogan) when Percy (Logan Lerman) and his pals turn up in the Underworld - only to turn on her husband. 

Persephone gives Percy Zeus's missing Master Bolt, which he'd come to retrieve, and buys the heroes time to escape using her magical peals that they'd gathered over the course of the movie. Her presence works out in Percy's, but this doesn't make sense in the world of Greek myth or the original novel.

In the book by Rick Riordan, Persephone doesn't appear at all, and the heroes have alternate ways of acquiring the three pearls, as well as the Master Bolt. This makes more sense, since according to the myth, Persephone only stays in the Underworld during the winter months.

There's no hand-waving this issue, either: just like the book, the film is explicitly set in summer, meaning Persephone definitely shouldn't be with Hades at this time. Had the movie followed the spirit of Greek mythology, the heroes' escape would have been impossible.

In William Shakespeare's Romeo and Juliet, Prince Escalus is the voice of authority in the family feud in the story. The characters Paris and Mercutio are his own family members. By the end of the play, Paris and Mercutio lose their lives, causing a grieving Prince Escalus to mourn them, saying he has lost “a brace of kinsmen.”

The 1996 Baz Luhrmann movie Romeo + Juliet alters Prince Escalus to be Captain Prince (Vondie Curtis-Hall), the chief of police. His familial relationship with Paris (Paul Rudd) and Mercutio (Harold Perrineau) is removed. Moreover, the film also adapts out Paris's death. Even with all the significant changes, Captain Prince utters the same line in the film's conclusion, which makes no sense. If Paris and Mercutio aren't his kin, nor is the former even dead, then it's unclear who the “kinsmen” are that Captain Prince has lost.

In You Only Live Twice, James Bond (Sean Connery) and Ernst Stavro Blofeld (Donald Pleasance) come face to face when the former foils Blofeld's plan of casting the world into war. Blofeld and Bond exchange dialogue and the villain explicitly escapes the hero by the film's end to leave no doubt of their antagonism for each other. For this reason, it's a wonder why Bond and Blofeld have no clue what the other looks like in On Her Majesty's Secret Service. 

At this point the books, Bond and Blofeld are aware of each other, but had never actually met in person - this makes it believable why they don't recognize one another face-to-face. Blofeld is an overarching antagonist in Thunderball, the preceding novel, and doesn't have a large part to play until On Her Majesty's Secret Service - where it's mentioned that he has had surgery to alter his appearance.

Confusion remains, since the films don't follow the same order as the books: You Only Live Twice was released first, despite the novel taking place after On Her Majesty's Secret Service. On the other hand, both characters are played by different actors in the latter film (George Lazenby as Bond, and Telly Savalas as Blofeld), which may help film fans swallow the inconsistency.

The 2009 film adaptation of Watchmen is set during an alternate history where the Cold War is still ongoing. The superhero Ozymandias, real name Adrian Veidt (Matthew Goode), takes it upon himself to avert all-out war between the US and USSR. To this end, Veidt hatches a plan to create an even bigger enemy that will necessitate an alliance between the two countries for their mutual survival.

In the comics by Alan Moore and Dave Gibbons, Veidt's diversion is simple: he fakes an alien attack by unleashing a squid monster on New York. Because an alien squid has no ties to either country, it makes sense why the USSR and US would join together without hesitation to fight the supposed extraterrestrials. However, the film goes for a more complex plot where Veidt places the blame on Doctor Manhattan (Billy Crudup) instead.

Here, Veidt orchestrates events to have Manhattan implicated in nuclear reactors exploding, causing the US and USSR to target him. While this isn't as silly as an alien squid, it has a clear plot hole: despite his supernatural powers, Manhattan is an American who works for the US military. Under this logic, Manhattan being accused would shift the blame on the US, making the USSR even more hostile toward them.

The film overlooks the US's culpability in Veidt's plan, which goes just as he wanted. Had the plot hole been addressed, though, Veidt would have caused even greater disaster than there was before.

Ella Enchanted is about the titular character's struggles with a gift that turns into a curse. As a child, Ella (Anne Hathaway) is presented with the “gift” of obedience from a fairy godmother, which causes her to obey any command she is given, regardless of her own wishes.

In the novel by Gail Carson Levine, Ella finally overcomes the curse because of a logical paradox. Meaning well, her love interest, Prince Char, orders her to marry him, which she wants to do. However, Ella also doesn't want to marry Char, because she knows their enemies would use her curse to take advantage of her position as royalty, ordering her around for their own gain. The struggle between wanting and not wanting something at the same time causes the spell to break, freeing Ella from her curse.

The movie eschews this logic in favor of a simple solution: Ella simply looks at herself in the mirror and commands herself not to be obedient anymore. Upon first glance, Ella's tactic is ingenious, seeing as she doesn't technically break any rules. However, if it were this easy to get out of the curse, it's hard to believe how Ella never thought to try it out in all the years she'd been suffering.