Continuity mistake: In the girls' lavatory, when Harry inspects the sink that Moaning Myrtle points out, the pattern of the stains on the porcelain are all visible. However, when the sink descends the stains are actually different. (01:57:55 - 01:58:55)
Continuity mistake: While in the girls' lavatory after Harry speaks Parseltongue, in the overhead shot as the sink top rises and in the following close-up of Harry, Ron and Lockhart, the boys stand close to the wall behind them. However, in the next overhead shot as the sinks seperate Harry and Ron are directly in front of the sinks. (01:58:40)
Continuity mistake: In the scene where the Chamber finally opens, we first see Harry, Ron and Professor Lockhart from the front, and Harry and Ron are slightly behind Lockhart, and in a position to threaten and guard him. When you next see them a moment later from behind, Lockhart is behind them and they are in no position to guard him. (01:58:45)
Visible crew/equipment: When Harry, Ron and Lockhart are in the girls' lavatory, Harry speaks Parseltongue to open the Chamber. Lockhart then tries to escape so the boys push him back. In this shot the white strips taped to the small black mat, which itself is taped to the floor for Rupert's mark, are plainly visible at his feet. (01:59:20)
Continuity mistake: In the girls' lavatory, Lockhart tries to bolt so Harry and Ron stop him and push him back. When Harry says, "You first," in this first shot his cloak not only drapes over the sink to his left, it's also under his hand's tight grip of the sink's wall. However in the next shot, still gripping the wall, his cloak now hangs behind him. Then after Ron says, "Better you than us," Lockhart's cloak is positioned the same way as the first shot. (01:59:20)
Visible crew/equipment: In the girls' lavatory Ron pushes Lockhart into the opening of the Chamber and in the shot looking up as Lockhart falls, at the upper right corner the side of a man's FACE is visible near the sink and when Ron jumps something else is there. (01:59:35)
Continuity mistake: When Lockhart falls down the hole into the Chamber of Secrets, we hear him hit the ground a second or two later. When Ron and Harry jump down, not only do they take longer to get down, they also slide down the pipe, rather than fall straight down. (01:59:40)
Continuity mistake: When Gilderoy jumps into the entrance to the Chamber of Secrets you see his cape go flowing up above his head. In a short second shot, taken from above, it's not. (01:59:40)
Continuity mistake: The distance between Harry and Ron when they're sliding into the Chamber of Secrets keeps changing. Harry jumps first, and Ron jumps a few seconds later, so there should be a little distance between them. But when they're sliding down, Ron is directly behind Harry. At the bottom though, Harry slides onto the ground a few seconds before Ron, meaning they're again some distance apart. (02:00:10)
Continuity mistake: The smudges on Harry's face and the dirt on Harry's cloak, pants, etc., change in consecutive shots, throughout the shots after the rock slide, within the Chamber of Secrets and thereafter. (02:04:00)
Visible crew/equipment: Upon entering the Chamber of Secrets, Harry spots Ginny and runs towards her. After the last close-up of Harry's face as he runs, there is shot that faces Ginny, showing Harry's back. At the very start of this shot, on the bottom left corner of the screen two overhead studio lights, other equipment and scaffolding are perfectly visible, reflected in the puddle to Harry's left. Later when he runs out of the pipe, towards Ginny, some light reflections are visible as well. (Visible on DVD fullscreen.) (02:04:40)
Audio problem: When Harry enters the Chamber of Secrets and spots Ginny lying on the ground, he runs towards her. However, the sound of his footsteps don't match his actual steps. (02:04:40)
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)
Continuity mistake: Tom Riddle says, "She won't wake" and walks toward Harry. When Harry says "Tom. Tom Riddle," the shot faces Harry and Ginny, and Harry's wand is lying on the open ground below the sole of Ginny's shoe. When Harry asks "Are you a ghost?" as the camera pans closer to Harry, his wand is conspicuously in a different place now, it is lying partially hidden under Ginny's robe above her right foot, right next to Harry. In the next shot after Riddle says, "A memory. Preserved...," the wand is gone from the previous shot's position. (Visible on DVD fullscreen.) (02:04:50)
Continuity mistake: When Harry says, "Tom. Tom Riddle," the shot faces Harry and Ginny, and Ginny's foot is parallel to the ground. In the next shot facing Riddle, Ginny's foot is perpendicular to the ground. When Harry asks, "Are you a ghost?" Ginny's foot is parallel. When Riddle says, "As poor Ginny grows weaker...," her foot is perpendicular to the ground once more and so forth. (02:04:50)
Continuity mistake: In the Chamber of Secrets and afterwards, the stain on Harry's collar is constantly changing. Some examples are the close-up as Harry leans over Ginny saying, "Ginny, oh please don't be dead. Wake up!..." and the close-up when Harry says, "Why do you care how I escaped? Voldemort was after your time." Also, in the close-up when Harry is crouching trapped with his back up against the grate, as the blinded Basilisk comes toward him, and then as he stands and looks at the Basilisk slithering away, up the pipe. (02:04:50)
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)
Audio problem: In the Chamber of Secrets, Riddle says, "You'll find I can be very persuasive." In the next shot facing Harry, the side of Riddle's face is visible and he is obviously speaking before we hear these words, "Not that she knew what she was doing." (02:05:55)
Continuity mistake: In alternating shots while Harry is in the Chamber of Secrets, he has a pimple above his lip; in other shots he does not. (02:06:40 - 02:11:30)
Visible crew/equipment: As Harry runs from the Basilisk after Riddle shouts, "Parseltongue won't save you now, Potter...," there is a close-up of the Basilisk's face. In the next shot, which faces Harry's back, the overhead studio lighting bar with multiple lights is reflected in the puddle in front of Harry. (02:09:55)
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.