(at around 1h 3 mins) During the Quidditch match, and the celebration afterwards in the Gryffindor Common Room, you can see the pupils chanting "Weasley is our king!". However, the soundtrack we hear is simply "Weasley! Weasley! Weasley!" repeated.
(at around 36 minutes) During Professor Slughorn's lesson, the students are instructed to brew a Draught of Living Death, the recipe for which "can be found on page 10". During the scene it is plainly visible that Hermione has her book open roughly in the middle, approximately page 200.
(at around 48 mins) When Harry opens the Prince's book after the scene in which Ginny takes it from him and reads aloud "This book is property of the Half-Blood Prince", the camera pans across the pages and briefly shows a page reading "Sectumpsempra. For Enemies". The first word is actually "Sectumsempra", not "SectumPsempra".
At around 1 hr 55 mins, when Dumbledore produces Tom Riddle’s diary for Harry, he calls it a Horcrux; however, he ought to have said 'was', as the diary was destroyed in Harry Potter and the Chamber of Secrets (2002), so it can no longer be a Horcrux.
When Snape accepts the Unbreakable Vow from Narcissa, he pledges certain things to her concerning her son, Draco Malfoy. However, Bellatrix tacks on a final clause that, should Draco fail, Snape must undertake the task Voldemort wishes Draco to perform. This directly contradicts the Dark Lord's orders — a fact all three present acknowledge they were aware of beforehand. Snape even says, "I can't change the Dark Lord's mind". It represents a fault in characterisation for all three to conspire against the Dark Lord's explicit wishes.
Although pupils largely flout Hogwarts' dress code when not in lessons, it remains uncharacteristic of Draco Malfoy — a pure-blood supremacist and Muggle-hater — to wear a Muggle-style suit rather than the customary wizarding robes.
(at around 2 hours 5 minutes) After Harry takes a sip of potion from the basin, a scoopful still remains in it. However, after Dumbledore drinks it the basin appears empty and Harry retrieves the locket from the now-empty basin.
(around eight minutes in) When Dumbledore puts the Muggle house "back in order", the clock clearly shows 10:35pm. However, the waitress Harry meets at the sandwich bar said she'd be off at "11pm", yet Harry and Dumbledore spot her and her colleague locking up the premises before they leave the railway station.
(at around 2 minutes) During the collapse of the Millennium Bridge, the structure is initially crowded with people, including many schoolchildren, crossing it. As the bridge begins to wobble, people start to stumble and fall. When the bridge is viewed from above, seconds later as it is destroyed, there aren't any people on it.
(at around 2h 10 mins) In the wide establishing shot just before Snape casts Avada Kedavra, the tower's safety railing is clearly visible immediately behind Dumbledore. Yet when the camera cuts to Harry's perspective as Dumbledore is struck by the spell, the railing has vanished and Dumbledore falls straight off the edge of the tower where it had been.
(at around the 50-minute mark) At the Three Broomsticks pub, Slughorn spills some of his drink onto the table and onto Hermione. Yet about a minute later, when the table is shown from the side where Slughorn had been sitting, it is dry — and no one has produced a wand to magically clean it.
(at around 1 hour 45 minutes) As Hagrid mourns over Aragog's body, Harry stands beside him. In the distant shots Harry's head is clearly above Hagrid's elbow; however, in the close-ups his head is below Hagrid's elbows.
During the pursuit through the cornfield when Death Eaters attack the Burrow, after Ginny and Harry stand their ground before the Order arrive, Harry is clearly seen pointing his wand. As the Order arrive and complete the protective ring, he is shown taking his wand out of his pocket.
In Fred and George's joke shop Ron enquires about the price of an item; the twins answer 'five galleons'. The twin closest to Ron is shown leaning on the bannister, but in the following shot his position has changed.
In the scene where Dumbledore and Harry meet Slughorn in the deserted house, several piano hammers are scattered on the floor. Those hammers are from an upright piano, yet the "restored" instrument shown later in the scene is a grand piano.
While Dumbledore and Harry discuss Horcruxes, Harry's hair appears neatly combed in one shot; when the camera cuts to a profile view, it looks tousled.
In the Christmas scene at the Burrow, while Harry, Lupin, Tonks and Mr Weasley are discussing Snape, take note of the trays of sweets and baked treats on the table. When their conversation finishes and Ginny comes over to sit and offer Harry a bite, a space on the table suddenly appears for her to set down her tray just as Ron sits between Harry and Ginny.
When Ron takes a seat with Harry and Hermione in the Great Hall before the Quidditch match, the bowl or spoon can be seen either immediately beside Hermione's left hand or positioned further away, depending on the camera angle.
In the Weasleys' sitting room, while Harry, Arthur, Nymphadora and Lupin are talking, the shot looking towards Lupin shows one of Harry's shoelaces undone. After a brief cut to a shot facing Nymphadora and Arthur (where Harry's hands are visible), it returns to the original angle and the shoelace has been tied. (This has no connection to Ginny tying Harry's shoelace much later.)
The pane of glass shattered in the Great Hall's window behind the staff tables looks slightly different between the moment Bellatrix smashes it and the later shot of the empty Great Hall.
During Potions class, just before the pupils go to their cauldrons to brew the Draught of Living Death, Hermione stands in front of Harry, but in the long shot she immediately appears at his side, then she's suddenly back in front of him again.
(at about 37 minutes) During the Felix Felicis scene, when Slughorn hands it to Harry, he holds it with his hand beneath the bottle. In the following shot, his hand is above it.
(around the five-minute mark) When Harry and Dumbledore pause and stand side by side before they approach the house where Horace Slughorn is hiding, the top of Harry's head, as seen from behind, sits below Dumbledore's shoulder. In the subsequent shot, shown from the front, Harry is noticeably taller — his nose reaches Dumbledore's shoulder — even though they do not appear to have moved.
When Death Eaters reach Diagon Alley, there aren't many people about; but after they turn up with Ollivander, the alley becomes crowded straightaway.
At Aragog's funeral there is a long shot of Slughorn, Hagrid and Harry standing beside Aragog. However, from that vantage point Aragog is not visible; given the angle you ought to be able to see Aragog's body.
When Dumbledore and Harry first arrive outside Slughorn's temporary lodgings in Budleigh, Babberton, Harry appears so short that he only reaches about the level of Dumbledore's shoulders (likely the actor's stand-in); but in the subsequent shot facing them his height returns to normal, roughly level with the Headmaster's eyes.
At the beginning of the Potions lesson in the film, Hermione and Lavender are shown standing beside one another while Professor Slughorn teaches. Yet within the opening minute or two of the scene they are pictured some distance apart; in the very next cut they are standing almost shoulder-to-shoulder, with hardly any space to move. They stay in that close arrangement for the remainder of the scene, although the initial gap between them is visible during the first few minutes of the lesson.
During the Death Eaters' attack on Ollivander's, the scattered debris, the flames and the bodies on the ground differ between the overhead shot and the subsequent close-up.
In the Great Hall, when Ron sits down with Harry and Hermione before the Quidditch match, the newspaper Hermione is reading repeatedly shifts from her hand to tucked under her arms and back again between cuts.
In the Potions lesson, when Slughorn produces the Felix Felicis vial he turns to face the class and raises it so everyone can see, but in the subsequent shot that faces him he is shown holding only the very tip of the vial's base.
When Ron is frothing at the mouth, the froth appears in some shots and is absent in others.
At the Muggle orphanage, in the corridor, when Mrs. Cole says, 'Tom, you have a visitor,' Dumbledore's scarf is slung at an odd angle, but in the following shot, with the camera facing him, the scarf sits correctly.
Whilst Dumbledore approaches Slughorn, who is masquerading as a chair, the appearance of both the sheer and the opaque curtains alternates — also note the presence or absence of holes between Slughorn's close-ups and wide shots.
In the scene before the Quidditch match, as Ron, Hermione and Harry are talking and Ron believes Harry has slipped something into his drink, Ginny's position varies between shots: in some angles she is sitting directly beside Harry with their arms only an inch or two apart, while in others Ginny's arm is nowhere to be seen even though they are close enough that she should be visible.
At the Burrow, during Harry's conversation with Lupin, Tonks and Arthur — and later when Ginny sits beside him on the sofa — the orange throw draped over the arm of the sofa to Harry's right shifts forward, then back, then forward again, and so on.
After Harry and Dumbledore return from the Horcrux cave, Dumbledore sits down with his arm draped round Harry's neck. When Dumbledore asks Harry to go and fetch Snape, that arm suddenly vanishes, and there was no time for him to have moved it.
At the Three Broomsticks, when Slughorn knocks his drink over, the froth around his fingers vanishes and reappears repeatedly.
After Hagrid faints in his hut, when Harry tells Slughorn about Lily's sacrifice, the vegetables on the shelves behind Harry change places.
As Dumbledore leads Harry to meet Professor Slughorn, a copy of the Daily Prophet lies on the floor amid scattered debris — the piano's hammer is among the items and its appearance varies between shots.
[SPOILERS] Snape killing Dumbledore is revealed to be part of a wider, more convoluted scheme orchestrated by the forces of good. That plan depends on the conspirators somehow being certain that Draco will not undergo a crisis of conscience when Dumbledore presents him with a way out.
As Dumbledore and Harry approach Slughorn’s armchair, a white lampshade sits on the shelf to the left, its edge projecting over the rim. When Slughorn gets to his feet and goes to the door to lock it, the lampshade is positioned further back on the shelf.
When Ginny snatches 'Advanced Potion Making' from Harry in the common room and says "Who's the Half-Blood Prince? That's what it says right here: 'This book is the property of the Half-Blood Prince'", she opens it to a random page roughly in the middle of the book. However, when Harry looks, the words 'This book is the property of the Half-Blood Prince' appear on the first page. There is a continuity error, as she is seen flicking between pages over a series of very brief cuts.
In the final moments, when Harry brushes hair from Dumbledore's face in a close-up, a few strands remain; as the camera pulls back to Dumbledore, different strands are seen across his face.
When Ginny snatches the Half-Blood Prince's potion book from Harry's hand, before he rises from leaning against the sofa on the floor, she is not to be seen in the chair at the extreme left of the frame. As Harry moves around the sofa whilst talking to Hermione, she is suddenly seated in that same chair.
As Dumbledore speaks to Harry about Horcruxes, Dumbledore's hair looks windswept and untidy in one shot, yet appears tidy in the next.
At Slughorn's party, a photograph of Harry and Slughorn is taken. The background, however, is entirely different before and after the flash, with insufficient time for it to have changed.
In the Great Hall, from the moment Hermione strikes Ron with the book until Harry (with a bloody nose) joins them, the spoon in Hermione's bowl frequently faces the opposite direction when seen from different camera angles.
In Potions class, during the lesson when the students are brewing the Draught of Living Death, as Harry tells Hermione, "Crush it, don't cut it," the way he holds and squeezes the Sopophorous Bean suddenly changes between shots.
In the scene featuring Weasley's Wizarding Wheezes, as the camera pans up the shopfront the shop name in gold lettering can be seen. However, when Harry, Ron and Hermione leave the shop to follow Draco Malfoy, the name is no longer visible.
During the dessert at Slughorn's dinner party, the serviettes hanging from the collars of some guests (for example Belby and Neville) change position between successive shots.
At the Three Broomsticks, Slughorn has a mug in his left hand while addressing Harry, yet when he utters 'Good to see you, Wallenby,' the mug is suddenly in his right hand and his left arm hangs by his side.
Atop the Astronomy Tower, shortly before Dumbledore and Harry set off to retrieve the locket, Dumbledore's hair is visible moving across his left shoulder in shots filmed from behind him.
At the Three Broomsticks, when Dean and Ginny are spotted snogging, Hermione's left arm is resting across the table in front of her; in the shot facing her both arms are down at her sides, but in the next shot her arm is back on the table.
Moments before Dumbledore and Harry set off on their Horcrux mission, the shadowy outline of a stagehand can be seen in the clock tower, ducking out of view as he realises he is being filmed.
The incantation Snape uses to treat Malfoy is "Vulnera Sanentur". It mends deep wounds, but it does not remove bloodstains from his clothing.
Some have argued that Aragog looks far smaller in this film than he did in Гарри Поттер и тайная комната (2002), but that is only partially accurate: spiders tend to shrivel quite rapidly after they die. On top of that, the people around him on this occasion are noticeably taller, and the camera angles used in his first appearance emphasised his size when he was alive. Taken together, these factors make the change perfectly reasonable and do not suggest any mistake or oversight on the part of the filmmakers.
(at around 2h 15 mins) Towards the end of the film, as everyone raises their wands aloft in tribute, many believed they saw Hagrid holding someone else's wand. However, on close inspection the hand is not Hagrid's but that of a nearby pupil.
(at around 8 mins) When Dumbledore first introduces Harry to Professor Slughorn, Slughorn's robe shifts colour on more than one occasion. This is actually caused by the fluorescent lighting outside Slughorn's house.
(at around 1h 40 mins) After Harry drinks the Felix Felicis, the vial appears to remain unopened while he is talking to Ron and Hermione. However, as he draws the vial away from his mouth, Harry can be seen replacing the stopper, creating the impression that the vial was never used.
In light of the war raging in the wizarding world, Felix Felicis ought to be readily obtainable, yet it's used only twice over the course of the story.
In a flashback, Tom Riddle asks Horace Slughorn about possessing multiple Horcruxes. However, according to additional lore later provided by J.K. Rowling herself, by the time he began wearing it it had already been made his second Horcrux (the first being the diary destroyed in the second film). He was already well on his way to his goal of six and had no way of turning back. This therefore raises the question why he would need Slughorn's opinion at that point.
According to Dumbledore, the ring that had once been a Horcrux had already been destroyed by the time he showed it to Harry. If it had been destroyed, it ought not to behave as though it were alive — for example, moving of its own accord.
Dumbledore was obliged to drink the potion to retrieve the locket from the cave. Harry later realises the locket is a fake, and that R.A.B. had already removed the true horcrux. Consequently, there was no need to replace the potion.
During the Slug Club dinner, Slughorn and the other guests are puzzled by the idea that Hermione's parents work in dentistry. However, in "Chamber of Secrets" Mrs Weasley's clock showing her family's whereabouts plainly reads "Dentist" as a destination, so witches and wizards clearly know what a dentist is.
(at approximately 1 hr 3 mins) During the Quidditch match, as Ron cheers a successful save, a gust of wind lifts his robes and the bicycle-style seat affixed to his broom is clearly visible.
(at around 1 hour 45 minutes) In the scene with Hagrid and Professor Slughorn, both are gesturing with their hands as they speak. Slughorn's hand often disappears or appears to pass straight through Hagrid's arm. The two were filmed separately to emphasise Hagrid's height.
Harry's glasses alternate between having lenses and being without them several times throughout the film. (The filmmakers arranged this so the lenses wouldn't reflect the camera whilst filming Harry).
(at around 5 mins) Early on, when Harry and Dumbledore first Disapparate, a wide shot captures them approaching the house entrance. In that shot you can see Dumbledore's shoes protruding from beneath his robe as he walks — he is actually wearing protective shoe covers, the kind the cast wear between takes to avoid damaging the set floors.
Once Professor McGonagall has sent Harry, Hermione and Ron back to their Gryffindor dormitories, Harry's forehead bears no scar.
(at around 2h 15 mins) Near the end of the film, when Harry is lying on the ground outside Hagrid's hut, Snape kicks Harry's wand out of his hand. As he does so, a square of neon tape is clearly visible, almost right in the centre of the shot, marking where Harry's wand had been placed so the actor Alan Rickman would know where to kick.
(at roughly 49 minutes) In the Weasley Brothers' shop scene, when they are showing Harry the Instant Darkness powder, a VFX layer over the case containing the powder (intended to darken the case from a dull grey to a true black) is clearly visible, extends beyond the edges of the case and shifts slightly during the shot.
(at around 36 minutes in) Inside Harry's "Advanced Potion Making" book, the text reads "How to Prepare the Draught of Living Dead [sic]", whilst the heading on the page itself is "Preparation of the Draught of Living Death".
