During Harry and Hermione's dance, the Nick Cave and the Bad Seeds track 'O Children' is audible on the radio. Yet the song was not written until 2004, whereas the film is set in 1997.
Throughout the books and films, characters in the Harry Potter series use quills exclusively for writing. Yet when Xenophilius Lovegood draws the Deathly Hallows symbol he repeatedly says "I need to get a pen." He repeats the word "pen" several times before he proceeds to sketch the symbol. Though it's hard to make out the implement he uses, it is clearly not a quill.
(at around 1h 35 mins) As Harry prepares to dive into the lake after the Sword of Gryffindor, he goes under with his spectacles on. They stay with him while he is submerged. When he resurfaces his vision is blurred and his spectacles are gone; he then picks them up from the ice, even though they are lying nowhere near the hole he dived through.
(at approximately 37 minutes) When the waitress in the café comes to take Harry, Ron and Hermione's order, she walks the same stretch twice.
(around 1 hr 50 mins) The sheet of paper on which Xenophilius Lovegood draws the symbol of the Deathly Hallows changes between shots. While he is sketching the symbol there is a smudge on the paper, but when the camera pans away and he speaks to Harry the smudge has gone.
(at approximately 48 minutes) When Hermione casts Expelliarmus at Mundungus Fletcher and takes his wand (in Grimmauld Place), she and Harry appear to move straight ahead almost instantly, which is clearly not Apparation.
SPOILER: In the book, Snape was only able to find Harry and bypass the security measures because Hermione had removed the portrait of Headmaster Phineas Nigellus Black from Sirius' house, and Black, while inhabiting his official portrait at Hogwarts, told Snape how to locate them. In the film they never removed or interacted with the portrait at all.
(at around 1h 7 mins) Shortly after Harry and Hermione are unable to destroy the Horcrux and Harry says "We need to keep it safe", he peers into the shard of his mirror; the camera is briefly visible in the reflection.
(at around 1 min) When Hermione first appears in the film she is holding a newspaper. The photograph of the Muggle family remains still despite appearing in a Wizard newspaper. One must assume that, since they are a Muggle family, they would not have had a Wizard photograph taken and so the image is a Muggle photograph, which explains the subjects' static poses. It is, however, apparent that the front-page photograph is animated.
When Harry asks, Hermione replies she does not know how long the Polyjuice potion they are using to infiltrate the Ministry will remain effective. Yet in Harry Potter and the Chamber of Secrets it is established that Polyjuice potion lasts for exactly one hour. J.K. Rowling has said that the potion's duration can vary depending on how well it is brewed.
The interior of the Dursleys' home appears to change. When Mad‑Eye Moody and his party arrive to take Harry, the room features burgundy wallpaper, a matching carpet and dark cupboards. Later, when a Death Eater turns up searching for Harry, the same location is shown with white walls and wooden floorboards. That sequence is actually a deleted scene, and the house shown isn't the Dursleys' at all but Hermione's. As Hermione never arrived at school—and being Muggle-born—she was likely still at home. After she cast a Memory Charm on her parents, they packed up and moved away.
After destroying the locket, Ron says: "Only three more to go." Some viewers object, noting that up to that point they had destroyed three Horcruxes — the locket, the ring and the diary — and that the previous film states Voldemort/Tom Riddle intended to make seven, which might suggest there were four left. That, however, is a misreading: Voldemort split his soul into seven pieces, six of which were stored in Horcruxes while the seventh remained in his body. Having already destroyed three Horcruxes, there were therefore only three more to find and destroy, so Ron's line is correct.
Voldemort leaves Nagini in Godric's Hollow, disguised as Bathilda Bagshot, to lie in wait for Harry's arrival. He could not have known that Harry would need Bathilda, since at that point he was unaware of the Horcrux hunt. Voldemort did, however, predict that Harry might go to Godric's Hollow because that is where his parents are buried.
Nagini is a python. When Voldemort allows her to devour the human teacher, Charity Burbage, it should take roughly three weeks for her to digest the body completely. Yet in the subsequent scene with the snake — which is set about a week later — there are no visible signs that she has eaten an entire person.
When the Snatchers spot Harry, Ron and Hermione after they've apparated away from the Lovegoods' house, why do they flee instead of linking hands and apparating to another location?
The Tale of the Three Brothers relates that the first brother requested a potent wand. He used it to kill a wizard he wished to take revenge on. That same night another wizard stole the wand and stabbed the first brother. Because the wand had not been won in a duel, it could never become any other wizard's wand, including Dumbledore or Harry Potter, according to the Laws of Wand Allegiance.
When the decoy Harrys and their companions arrive at The Burrow, Lupin tests Harry to ensure that he is the genuine article. As the others begin to turn up, Kingsley Shacklebolt tests Lupin, but Lupin does not test him back. No one else is tested.
It's apparent that Harry's spectacles are missing their lenses in certain scenes of the film.
When Fred and George turn up at the Burrow after being pursued by the Death Eaters, their shorter "Harry" clothes still fit them.
(at around 1h 30 mins) While Hermione is reading Rita Skeeter's book, she informs Harry that she has worked out the boy in the photograph at Bathilda Bagshot's home is Gellert Grindelwald. As she hands the book to Harry, if you look closely you can spot an oval-shaped hole in the front cover where Dumbledore's moving picture would have been.
