Continuity mistake: In the Great Hall, when Lavender's eyes are shooting daggers at Ron and Hermione, Harry's arms/hands keep changing position on the table as the three of them speak.
Continuity mistake: At Aragog's funeral, there is a long shot of Slughorn, Hagrid and Harry standing by Aragog. However from this angle Aragog is not here. Given the angle you should be able to see Aragog's body.
Continuity mistake: At the Three Broomsticks, Slughorn is holding a mug with his left hand when he speaks to Harry, but when he says, "Good to see you, Wallenby," the mug is suddenly in Slughorn's right hand, with his left arm down by his side. (00:51:15)
Continuity mistake: In Potions class, when Slughorn removes the vial of Felix Felicis, he turns to face the class and holds the vial up for the class to see, but in the next shot facing him he holds only the very bottom point of the vial. (00:35:15)
Continuity mistake: When the Death Eaters attack Ollivander's, the debris/fire and the bodies lying on the ground differ between the overhead and next close-up.
Continuity mistake: At the Burrow, when Ron takes a seat between Ginny and Harry he is holding a pedestal plate full of pies, which change in the next shot facing the other way.
Continuity mistake: In Hagrid's hut, when Slughorn and Hagrid are drinking, the cups/bottle on the table change position between shots.
Continuity mistake: Aboard the Hogwarts Express, when Draco petrifies Harry he falls immobilized. Just as Draco kicks him, Harry's head is positioned farther out in the aisle, than previous and following shots. (00:26:40)
Continuity mistake: When Luna and Harry pass through Hogwarts gate, the parchment and wand in Flitwick's hands differs between shots.
Continuity mistake: When Ron is foaming at the mouth, the foam is either there or it's not, depending on the shot.
Continuity mistake: At the Muggle orphanage, in the corridor when Mrs. Cole says, "Tom, you have a visitor," Dumbledore's scarf hangs askew, but next shot facing him the scarf hangs properly. (00:40:05)
Continuity mistake: The glass that is smashed in the Great Hall's window behind the staff tables changes somewhat from when Bellatrix smashes it, and when we are shown the Great Hall empty.
Continuity mistake: When Dumbledore and Harry are talking about Horcruxes, Harry's hair is nice and combed in one shot. The camera cuts to a side view and his hair is now messy.
Continuity mistake: In the Great Hall, when Ron (wearing his Quidditch uniform) asks Hermione about the Slug Club, Ron's right arm lies on the table in front of him in shots from behind, but in shots facing him his right arm is down beside him.
Continuity mistake: When Hermione opens the locket to read the note, the locket and chain's position changes in her hand between consecutive shots.
Continuity mistake: At the end of the movie, there is a long shot of Hermione, Ron and Harry atop the Astronomy tower. In this long shot Hermione's hands are in different places compared to the previous close up.
Continuity mistake: During the Slug Club's dessert, as Slughorn speaks to the students, their ice cream, syrup, thin wafers, spoons, etc, change depending on the camera angle.
Other mistake: While Harry, Ron, and Hermione are walking back from the Three Broomsticks, Ron whispers to Harry about Hermione's earlier comment about snogging, and when we hear Ron say, "As if!" the subtitles read that Harry said it. (00:51:45)
Other mistake: After Ginny sees Hedwig and Harry's trunk at the Burrow, everyone gathers at the staircase and talks to Ginny about Harry's whereabouts, and when Hermione exclaims "Really?" we hear Harry answer "Really!" but the subtitles read that Ron answers Hermione. (00:13:00)
Other mistake: When Professor McGonagall is talking to the trio about the necklace incident and Professor Snape is walking by in the background, he stops just before she calls him over.
Answer: Leaving an untrained young wizard, who obviously has some behavioral issues and has no idea he is magical, alone in the Muggle world would be extremely dangerous. Dumbledore does not yet know that Riddle will become evil, but like any teacher, he wants to give a troubled youth an opportunity to find a new path in life.
raywest ★