Continuity mistake: Errol makes a mess with the chips and when Ron deals with the Howler, the mess on the table differs depending on the camera angle. For example, when the Howler says, "Ronald Weasley! How dare...," there is one kind of mess and then when it says, "..and it's entirely your fault!" there is another mess, but when the Howler shreds itself, the mess is the same as the first shot. (00:34:00)
Continuity mistake: In the duel scene between Harry and Draco, Lockhart walks in front of Harry to cast his spell on the snake. Lockhart is standing between Harry and the snake, though when the snake lands, Lockhart is far behind Harry, back in his original position. (01:08:05)
Revealing mistake: After Harry yells, "Wood, look out!" Harry ducks to avoid the Bludger and flies away. In the following close-up of Harry, there are two reflections in each of the lenses of his glasses. The reflections were added deliberately for this shot, however, as he sweeps around the pitch, changing direction as he goes, the reflections should reflect the change in scenery around him, but it does NOT. (00:54:35)
Audio problem: At the Weasleys, as they read the Hogwarts' letters, Mrs. Weasley picks up Harry's letter and we hear her say, "We'll manage," though visibly she does not say that, she is saying something else. (Visible on fullscreen DVD - viewed on PC.) (00:13:15)
Revealing mistake: When Harry puts the sword through the head of the basilisk, you can see that the front pair of fangs are to the left of his right arm that the fang goes through. With the way Harry pulls out the sword it is impossible that the fang would go through his right arm. (02:13:50)
Other mistake: When Tom said that he set Hagrid up Harry said that Hagrid is his friend. In Icelandic subtitles it is translated that Harry is his friend.
Continuity mistake: In the second to last scene when Dumbledore is talking to Harry and Ron, Ron's hair is a bit roughed and has a big cowlick. In the next shot, the cowlick is gone and both Ron and Harry's hair is neat. (02:18:20)
Audio problem: As Harry escapes into the car, Ron leans forward, puts his left arm in front of Harry and although we hear him say, "I've got you, Harry!" Ron's lips remain apart, with teeth are clenched, and his mouth does not move. (00:09:45)
Continuity mistake: In the dueling scene with Snape and Lockhart, when Snape says expelliarmus then does his wand movement, the camera leaves him after he has stopped moving his wand to look at how it goes after Lockhart, you can see Snape still in the background and he has not finished moving his wand. (01:05:35)
Continuity mistake: In Dumbledore's study, after speaking with the Sorting Hat, Harry walks toward Fawkes. As he passes Dumbledore's desk, on the corner of the desk there are some books lying on the side of the crystal ball. Then in the overhead shot as Harry says, "Your bird... He just caught fire," the books lie diagonally at the corner in front of the crystal ball. (01:14:50)
Continuity mistake: When Ron and Harry's belongings are being thrown out of the trunk of the car, the way they fly out and their positions on the ground are different in all of the shots. (00:28:10)
Continuity mistake: After arriving at Diagon Alley, Hermione runs up to Harry and Hagrid. In the wide shot as she says, "Harry!" there is a man with a red hat, holding an owl, to Harry's left and hanging in the doorway are beads that are pulled to the side door frame. In the close-up when Hermione says, "It's so good to see you," as that man enters the store the beads are hanging straight down. The beads are pulled up again in the next wide shot when they say goodbye to Hagrid. (00:17:25)
Continuity mistake: When Harry first hears the whispering voice and is walking down the hallway feeling the wall as the voice gets louder. Notice he has a round red mark on the back of his right hand. In the next shot it's gone. (00:43:00)
Continuity mistake: Just as Ron turns downward when Harry says 'we need to find the train', Hedwig looks out the window behind Ron. In the next shot, her entire body is facing the window behind Harry. (00:23:25)
Continuity mistake: When Harry stabs the diary, it is completely soaked in ink, but when Professor Dumbeldore shows it to him it is partially dry. I doubt that Harry had time to escape the chamber, try and wash off the ink, and go to Dumbeldore's office. We see that stabbing the diary renders it powerless, so it can't have soaked up all the ink.
Continuity mistake: In the scene where the car drives away, there are no tracks left in the grass from when the car drove away from the Whomping Willow tree, but the car leaves tire tracks in the grass as it drives away after dumping Ron and Harry. (00:28:05)
Continuity mistake: When Tom Riddle takes Harry's wand in the Chamber of Secrets and Harry says "Give me my wand, Tom," his arm goes from being at his side to outstretched to back at his side in successive shots. (02:05:30)
Continuity mistake: When Ginny runs downstairs to ask her mum for her jumper, the boys are eating breakfast at the table, Harry and Ron are sitting on one side, and directly opposite them are Fred, George and Percy sitting on the other side. When they are joined by Arthur Weasley, who sits at the head of the table, as he speaks to Harry and the boys we see the empty space, an unused knife and fork on Arthur's left hand side, though the twins were sitting there eating breakfast, as was seen previously. When Errol comes with the post, the twins are seen at the end of the table once again eating their breakfast, opposite Harry and Ron. (NOT visible on the DVD widescreen) (00:12:40)
Audio problem: When Harry, Hermione and Ron discuss Tom Riddle and Hagrid's supposed link to the Chamber of Secrets Hagrid overhears something and asks if they were talking about him. Harry, Hermione and Ron all turn round and we hear them say, "No!" at the same time. If you watch carefully, Hermione says, "No!" slightly afterwards, but no sound comes out. The line has been dubbed so that they all say it in unison. (01:30:16)
Continuity mistake: When Harry just enters the Chamber he is running towards Ginny and drops his wand behind him, then Tom Riddle comes out and is to the front/side of Harry,he then picks up Harry's wand but he never walked behind Harry to pick it up, so the wand was in the wrong place. (02:04:45)
Answer: Yes. It's a common occurrence in a lot of movies for actors to forget their original lines so they improvise something to help move the scene along and not break character. Tom did this because he forgot what his original line was.