With the unique Wizarding World of Harry Potter, British writer J.K. Rowling managed to successfully cement herself as one of the most beloved authors of all time. The amount of research and creativity that went into the series is mind-boggling, which explains why, over 20 years since the first book was released, the Harry Potter franchise is as popular as ever.
As a book that finally ties the entire Harry Potter story together and provides fans with satisfactory closure, Harry Potter and the Deathly Hallows was the most anticipated and lauded installment of the franchise and was subsequently split into two movies. However, as her previous work, it's not free of plot holes.
Hermione claiming she's never done a memory modification
An oversight on the author's part, Hermione clearly stated that she's never done a memory modification before when she proceeded to wipe the memory of one of the Death Eaters the trio faced in a London cafe.
However, this is obviously not the case since she had done one of the biggest memory modifications you can do by completely erasing herself from the memories and household pictures of her parents just earlier in the film. And in fact, the obliviate charm is frequently used in memory modifications, making this an obvious plot hole ...unless Hermione somehow managed to obliviate herself forgetting what she had done to her parents? This brings us to our next point.
How did Hermione's parents explain her bedroom and all the stuff she left behind?
If Hermione did successfully obliviate her parents, removing every semblance of her from their minds and memories, how, then, would they explain to themselves a perfectly furnished female bedroom upstairs?
Moreover, it seems that Hermione didn't think the whole thing through, leaving her parents in denial they ever had a daughter when questioned about the little girl that grew up with them by all of their friends and neighbors.
Using the Polyjuice potion to trick wizarding institutions
The famous Polyjuice Potion is the subject of much debate and controversy itself, yet this time we're focusing on the logic of using it to enter established wizarding institutions such as the Gringotts Bank or the Ministry of Magic. Already in book one, Gringotts was introduced as the safest place in the Wizarding World (except Hogwarts, according to Hagrid), yet a pair of underage wizards were able to walk in a disguise and simply wave their wands with he Imperius curse and access the vault of one of Britain's most prominent dark witches.
Equally ridiculous is the trio's ability to use the potion's power to disguise themselves as the employees of the ministry and walk in completely undetected until the potion itself started wearing off. You would think that in the world of Harry Potter, where the Polyjuice Potion is being so frequently exploited, the most guarded institutions would have at least some kind of defense to spot common magic.
Harry, Ron, and Hermione struggling to find food in the final book
The trio's quest to find and destroy all the remaining Horcruxes before Voldemort finds Harry was a long and daunting one, made worse by the adverse living conditions and food sparsity. To deal with their hunger, the protagonists had to go scavenging for food, often not having enough to go by.
This, however, is ridiculous, since we learned a long time ago that, while food cannot be magically created, wizards can use spells to duplicate or manipulate the size of the food, which essentially means the trio would never go hungry. We think that Hermione, bright as she is, would think of this obvious solution, and yet she didn't.
Why Didn't Bellatrix use magic to identify Harry in the Malfoy manor?
This one just makes no sense at all. In Harry Potter and the Deathly Hallows Part 1, our three favorite wizards are captured by a group of Death Eaters, so Hermione has the bright idea of using a spell to disfigure Harry's face so he can't be recognized.
The three are captured and taken to Malfoy Manor, only to find Bellatrix struggling to figure out who the third member of the party is. But, why didn't she just use magic to get Harry's face back to normal? For a wizard or witch in the Harry Potter world, it should be like second nature to try to use magic to solve a trivial problem like this.
Harry using three wands to cast a powerful spell
After being captured together with Hermione and Ron at the Malfoy Manor in the books, Harry finds three wands which he uses together to produce one powerful Stupefy charm against the superhumanly strong Fenrir Greyback - a Death Eater who happens to be the same Werewolf who gave Remus Lupin lycanthropy and badly scarred Bill Weasley's face.
We have no idea why Rowling decided to add this short and pointless detail in the books, as it makes for a ridiculous plot hole. If using multiple wands simultaneously could actually give someone as young and unpracticed in magic as Harry the ability to triple the power of his spells, then Voldemort would probably be carrying around a huge stack of wands tied together with a rubber band.
Where did Draco and Narcissa get their wands during the Battle for Hogwarts?
After the skirmish in Malfoy Manor in the Deathly Hallows Part 1, Harry takes Draco's wand, prompting Draco's mother Narcissa to lend him her own. Fast forward to Deathly Hallows Part 2, and Draco loses his second wand after Vincent Crabbe set fire to the Room of Requirement by losing control of the Fiendfyre spell. At this point, both Narcissa and Draco are left wandless.
A bit later in the movie, Harry finally goes to face Voldemort in the Forbidden Forest where he faces death. Checking him for signs of life, Narcissa was to originally retrieve Draco's wand from him, but in the movies, Harry holds on to this wand when he shows himself alive before the final battle with Voldemort. This wand was then supposed to be given to Draco by Narcissa when Voldemort called him to join him. However, since in that scene both Narcissa and Draco are shown holding the same wand that is still in Harry's possession, there's a massive continuity error going on.
How did Dumbledore not defeat Voldemort using the Elder Wand?
By now, we all know the legend behind the great Elder Wand and how it makes its master virtually unbeatable. We also learn that the very same wand in question has been in the possession of Albus Dumbledore this whole time. This much as been revealed in Harry Potter and the Deathly Hallows Part 1.
However, earlier in Harry Potter and the Order of the Phoenix, Dumbledore duels Voldemort using the aforementioned Elder Wand and visibly struggles, ultimately almost losing the duel before Voldemort apparates away upon the arrival of the Minister of Magic. Does this make Dumbledore an extremely unskilled duelist? Probably not.
Lily Evans's Eyes changing color throughout movies
For some fans, this aspect of the last movie was a big annoyance. When young Lily Evans is shown through Snape's memories, a focus on her face clearly and deliberately shows the young actress's dark brown eyes, when in fact, everyone knows Lily's eyes are supposed to be green.
Over the course of the 7 books, we've constantly been hearing how Harry looks like his father, except for his eyes, which are his mother's. This oversight and a lack of effort on the movies' part when showing young Lily Evans cannot be ignored.
Snape remembering moments with Lilly he wasn't there to witness
In the final movie, Harry Potter and the Deathly Hallows Part 2, Harry finally discovers the truth about Severs Snape and, while the scene showcasing Snape's memories and feelings for Harry and his mother Lily are touching, we can't ignore the fact that they show Lily telling baby Harry to be safe and be strong and then being murdered by Lord Voldemort before Snape actually arrives to witness the scene.
Likely a small compromise that was included for the sake of stirring emotion, but a plot hole nonetheless.