Continuity mistake: During the first potion class scene during the movie, Hermione and Lavender are seen standing next to each other while being taught potions by Professor Slughorn. However, within the first minute or so of the lesson, Hermione and Lavender are standing far apart, then in the next shot, they are standing close together, with what looks like barely any space to move. They remain like this for the rest of the scene, but you can see the gap between the two within the first few minutes of the class.
Continuity mistake: In the Great Hall, from the time Hermione hits Ron with the book to when Harry (with bloody nose) joins them, the spoon in Hermione's bowl repeatedly faces the opposite way depending on the angle of the shot. (00:29:35)
Continuity mistake: The very first shot of Malfoy pulling the tapestry off the Vanishing Cabinet (after tossing a green apple in his hand) is used once again later (after Harry and Luna head off to Slughorn's party), when he is pulling the tapestry off again before placing a green apple in the Vanishing Cabinet. Note the same poof of dust, angle in which tapestry falls, and Draco's body position.
Continuity mistake: When Dumbledore and Harry enter the muggle house to find Slughorn the lights are all out; the only illumination comes from their wands. They enter the hallway, then both turn towards the living room with their wands in front of them. Despite this, the wall behind them is illuminated without either of them casting a shadow. The lighting in the hallway is obviously coming from a different source, not the wands. Can't be moonlight - it is a bright white light shining directly on the wall that was not visible when Harry and Dumbledore first entered the flat.
Continuity mistake: At the Three Broomsticks, when they notice Dean and Ginny snogging, Hermione's left arm is leaning across the table in front of her, then both her arms are down at her sides in the shot facing her, but next shot, her arm is on the table once again. (00:50:25)
Continuity mistake: When Dumbledore and Harry approach the Slughorn armchair, on the left there is a white lampshade lying on the shelf hanging over the edge. When Slughorn stands up and walks to the door to lock it, the lampshade is farther back on the shelf.
Continuity mistake: 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 at a random page in the middle of the book. When Harry sees the words 'This book is the property of the Half-Blood Prince', they are written on the first page. Also, the continuity is wrong as she is shown to switch pages between very quick shots.
Continuity mistake: At the end when Harry moves the hair from Dumbledore's face in the closeup, several strands of hair are left. When they pan back to Dumbledore, different strands of hair are across his face.
Continuity mistake: When Ginny rips the Half-Blood Prince's potion book out of Harry's hand, before Harry gets up from leaning against the couch on the floor, Ginny is nowhere to be found in the chair on the very far left of the screen. As Harry walks around the couch while talking to Hermione, she is suddenly sitting in the same chair.
Continuity mistake: At the Weasley's house when Hermione, Ron and Harry are talking about Dumbledore, Hermione's legs and the little table change position between shots. (00:14:30)
Continuity mistake: In the scene where Dumbledore and Harry meet Slughorn in the desolated house, some piano hammers lie on the ground. These hammers are from an upright piano but the "restored" instrument later in the scene is a grand piano. (00:06:25)
Audio problem: When the trio are on the Hogwarts Express, we hear Harry say "What was Draco doing with that weird looking cabinet and who were all those people" but the subtitles say it was Ron who said that.
Continuity mistake: Tied round Dumbledore's beard is a thin silver strand, with dangling silver balls, that changes position and the height of the silver balls differ in consecutive shots, depending on the camera angle throughout the film. For example, when Dumbledore and Harry first pay a visit to Slughorn.
Continuity mistake: When Dumbledore brings Harry to meet Slughorn, the Daily Prophet is lying on the floor amongst debris, including the piano's hammer, which differs between shots. (00:06:50)
Continuity mistake: In Potions class, when the students prepare the Draught of Living Death, as Harry tells Hermione, "Crush it, don't cut it," the way he holds/squeezes the Sopophorous Bean has instantly changed from the previous shot.
Continuity mistake: At the Burrow, when Tonks and Lupin are at the front door with Mr. and Mrs. Weasley, it cuts to an exterior shot of Harry looking out the window with his arm leaning across his knee in front of him, but in the next interior shot his arm is down at his side.
Continuity mistake: At Slughorn's party, Harry and Slughorn have their picture taken. Before and after the flash the background changes completely without enough time to change.
Continuity mistake: When Dumbledore is talking to Harry about Horcruxes, Dumbledore's hair is blowing and messy in one shot, but fine in the next shot.
Continuity mistake: At the diner when Harry walks toward the windows, in the close-up of a window through which we see the distant platform (before Dumbledore appears), the style of the window's muntins (sash) around the glass panels is quite different in this close-up, than in the previous shots of the windows. (00:04:00)
Continuity mistake: On top of the Astronomy Tower, before Dumbledore and Harry leave to retrieve the locket, Dumbledore hair moves in front of his left shoulder in shots behind him. (01:57:35)
Chosen answer: Snape wants to know how Harry knew Sectum Sempra. As shown by him using Occumelancy to see where his copy of Advanced Potion making is. But at the same time, if Snape punished Harry for a spell in a book, Harry could show it to Dumbledore, who would recognise Snape's handwriting. Additionally, Harry was certainly punished in the book - he got detention with Snape every Saturday for the rest of the term. The movie most likely had to cut this for time issues, and also perhaps because the scene is more dramatic if Snape only silently glares at him.
Ssiscool ★