At the beginning of the movie Harry talks to Hedwig, apologizing that he can't let her out of her cage because he isn’t allowed to do magic outside of school.  What happened to the old fashion way of opening the cage with a key, which just happened to be in the lock!?

While Harry is talking to Dobby in his room one second the flag on his wall is pinned slightly towards the center so that a bit of the end is hanging and than later in the scene the flag is perfectly pinned to the end.

When Dobby explains to Harry why he hid his letters, you can see that the drawers in the dresser behind him are neatly closed (with the exception of the bottom one, which is slightly open). However, in the next shot when Dobby runs out the door with Harry chasing after if you look closely you see that the drawers are slightly open and uneven.

As Harry chases Dobby into the hallway, he lands behind Dobby with knees bent and one hand stretched forward and the other back. The shot changes and focuses on Dobby. But when it returns to Harry, he is in a completely opposite stance to his previous one.

In the beginning of the Chamber of Secrets when Fred, George, and Ron pull the bars from Harry's window, the bars from the window fall near the bush under his window. However, when Vernon falls from the window, the bars from Harry's window are gone.

In the first movie, Harry gets a Nimbus Two Thousand, which also appears in CoS when he’s playing Quidditch.  Why is it then that Harry doesn’t put a broom in the Anglia on the way to the Burrow, isn’t carrying a broom on his trolley on the way to the platform, and no broom gets thrown out of the Angelina after it gets beaten up?

When Ron and Harry land near the burrow they go past a shed, but when the shot changes they are driving by the shed.

In the same shots as above, we can see a shadow to the southwest of the car.  In the next shot, the shadow is more under the car.

When George, Fred, Ron and Harry return to the burrow and you see the Weasley Clock if you look closely you'll see that Molly's, Percy's, and Ginny's hands are on garden.  Still somehow Percy and Ginny were able to appear in their pajamas (Ginny coming down from upstairs) as if they had just woken up.

When Harry arrives at the Weasley's house, we see a shot of the fireplace that he is going to travel up. There is no pot of Floo Powder or a bracket to hold it that is later visible when they’re about to travel to Diagon Alley.

When Errol brings the Hogwarts letters to the burrow, Percy takes them and hands everyone one, then it cuts and you see Fred/George passing another letter to George/Fred after he already got one.

When Ron steps into the fireplace to use Floo Powder, he supposedly takes a handful of the sand, but if you look closely, no sand is slipping out of his hand, he just crinkles his hand.  But in the next scene, he somehow has the sand, dropping it into the fire.

In the scene when Harry and the Weasleys are going to Diagon Alley, Mrs. Weasley urges Harry into the Fireplace. As she does this she holds the floo powder can out with only one hand and you can see her other hand down at her side. Then there is a close-up of the can, and she is shown holding it with both hands.

In the scene where Harry slides out from the fireplace into the dark shop, he quickly exits through the front door.  Just before he walks out, you can see a bright and shiny sidewalk outside, not like the dark and dingy surroundings that he walks out to.

Not only does Dobby block Platform Nine and Three-Quarters, but after impact and during a cut-scene, Hedwig's cage is closed, after being blown open from impact.

When Harry falls out of the Anglia and is holding on to Ron, on a shot more to the end of that part, packages all of a sudden appear right behind the seat.  These magical packages also somehow don’t fall out of the car.

When Harry and Ron flew over the lake to Hogwarts in the flying car, there was no reflection of the car on the lake.

When Ron's wand breaks in the car, you see him toss it away, but when the car chucks everyone and everything out, the wand is not shown being thrown out.  Then later he has his wand again.

When Harry and Ron land in the Whomping Willow, one shot from inside the car shows a branch coming through the rear window, and then pulling right out again. In the next shot (from outside the car) the branch is shown still coming out.

When a branch from the Whomping Willow breaks into the back window of the car, you can see a little bit of Hedwig's cage.  Even though it’s tipped over you can still see enough of it to tell that Hedwig isn't in it.

While the Anglia is getting beaten to a pulp by the Whomping Willow, Hedwig isn't moving at all.

When the Anglia falls out of the Womping Willow and drives a little bit away with Harry and Ron, it makes no track marks.  There are only marks from the wheels when it drives away on its own.

After the car chucks out Harry and Ron, the car drives away and Ron and Harry chase after it. If you look closely you can see the shadow of someone driving the car.

When the flying car throws Harry and Ron out of the car, and Harry is lying on the grass, you see that he starts getting up, but in the next wider shot he starts  getting up again.

When the Anglia starts driving off, its trunk is open.  Than we see Ron and Harry running after it and when it turns back to the Anglia, the trunk is closed.

The entire Herbology class should have feinted at the sound of the Mandrakes.  Seamus and Sprout have an entire conversation with them on.

When Errol flies away after delivering the howler his wing hits Hermione’s head.

When Lockhart lets the pixies out, you can clearly tell that Hermione knocked the books off the desk on purpose.

In the same scene, 2 of the pixies pull Neville up by his ears and hang him on a chandelier.  As the pixies were computer animated they had to put clips behind Neville’s ears to make it look like he was being lifted up by the pixies.  After he was dropped onto the chandelier by the pixies, his ears are still in a stretched position where the clips are.

When Oliver Wood and the team are walking to the Quidditch field to practice and they see the Slytherin team as well, in the left hand side of the screen Hermione puts her book beside her on the bench. When the shot goes completely to them, she puts the book down again.

The writing on the wall about the chamber being opened was way above Harry and Filch’s head. So how did Ginny grow so tall while writing it?

In the Polyjuice Book that Hermione shows Harry and Ron, if you look closely you’ll see that on the bottom of the 1st paragraph is written "...Into the form of an another". There is an extra ‘an’.

In the same book you can see pictures of all kinds of animals, but how is that relevant to the Polyjuice?  You’re not supposed to use it to change into animals.

During the scene in Transfiguration classroom, the students' positions in the class are constantly changing - for example, there is a blond girl sitting in the middle of the class in one shot sitting next to a girl who looks like Hermione from the back, then in another she is back in a corner and Neville takes her place next to Hermione.

One, two, three, ferreverto. Too bad the words aren't written on the blackboard in back of McGonagall when she's teaching. Instead, very strange figures that are actually backwards, as the film reel was flipped over for better picture, are what's there. The same explanation could be used for a later mistake regarding Harry's wand in his left hand.

When they are in McGonagall's class and she's talking about the Chamber of secrets, she mentions the fact about the purebloods. Hermione and Draco both look at each other (meaning that Draco had to look the other way completely from Mcgonagall), but in the next cut Draco is looking back at McGonagall.

In the Quidditch scene, the shadows of the goal posts keep changing direction.

When Harry is hit with the bludger, it knocks off his arm guard, and leaves this sort of glove (that reaches his elbow) that is tucked into his sleeve. After Harry falls the glove is over his sleeve, and after the bludger is destroyed the glove magically shortens and there is only his sleeve where the rest of the 'glove sleeve' was.

In the Quidditch scene when Harry breaks his right arm, he leans on it for a moment to help himself sit up and avoid the bludger.

When Harry drinks the Skele-Gro he spits almost all of it out, but Madam Pomfrey doesn’t tell him to drink more.

When Dobby visits Harry in the hospital, he bashes himself on the head with the bottle of Skele-Gro and Harry yanks it out of Dobby’s hands and puts the bottle down on the table at the foot of the bed. After he disappears and the shot changes, the bottle is back in its original place on the side-table at the head of the bed; the table at the foot of the bed is empty.

When Harry jumps onto his bed in the hospital wing after Dobby disappears again, it shows him jump on top of the covers. Less than a moment later, he has the covers over him. There is no way Harry can get under the covers in 3 seconds after landing on them.

In the Duel scene, Snape casts his spell against Lockhart.  Lockhart goes flying through the air, wand in hand.  The movie then cuts to a shot where Lockhart’s wand goes flying through the air out of his hand, then it cuts again to a shot where he lands wand in hand and finally cuts to Lockhart getting up without his wand.

When Harry curses Draco during their duel, Draco falls to the floor and his hair is messed up. When he gets back up his hair is slicked back again.

After the snake part, when Justin says, "What are you playing at?" to Harry, Susan Bones is about 3 feet away from Justin.  But when the scene cuts to Harry, then back to Justin, she is standing right next to him.

When Crabbe and Goyle reach for the cakes that Harry levitated, if you look at Ron and Harry in the background, you can clearly see that it's not Ron. He is several inches shorter, and his hair is floppy. In the next shot, it is Ron, and when they go back to Crabbe and Goyle, it's not again.

In the scene where Harry, Ron, and Hermione are drinking the Polyjuice Potion, Harry leans toward the mirror and starts to gag. You can see his shirt is half-unbuttoned. Then they cut away to another shot farther back and when they cut back to him,  his shirt is buttoned up, nice and neat.

When Harry and Ron are in the girls’ bathroom and find Tom's diary, it is night. Right before they go into the bathroom it’s daytime, you can see the sunlight coming through the windows.

The one tap at the sink opening for the Chamber of Secrets is overflowing when Myrtle cries, but when Harry, Lockhart and Ron go back later, the top does not work. You can see and hear Harry turning the tap and no water comes out.

When Harry and Ron are in the restroom, after they ran through the puddle at the beginning of the restroom, their shoes are not wet.

When Tom takes Harry to the past, and shows him ‘the capture’ he says that Moaning Myrtle's parents will be at school the next day.  But Myrtle's parents can't be at Hogwarts since Myrtle was muggle-born, and since her parents are muggles.  Muggles can't see Hogwarts.

In the scene where Harry and Ron are talking to the giant spider in the Dark Forest, Fang keeps changing places.  One second he’s about 2 feet away from Harry and one second later he’s right next to Harry.

After Harry and Ron found the piece of paper in Hermione's hand, they start walking along a corridor as Harry reads aloud. They walk towards the camera as the shot changes and Harry says 'spiders flee before it'. The movement of his lips doesn't match what he says.

Lockhart takes a few seconds to fall to the bottom of the Chamber of Secrets.  Harry and Ron take much longer.

When the Snake-bordered door to the Chamber of Secrets opens, and all the way through Harry's approach to Ginny, he's carrying the wand in his left hand.  Though, the wand when thrown down lands where his wand would have if it were in his right hand.  Apparently Dan's right hand would have blocked the snake-door from the camera or something, so he was told to hold it in his left. His right hand is his wand hand, though.

In the Chamber when Tom Riddle is telling the basilisk to attack Harry, right after the snake crawls, Tom looks it directly in the eye and doesn't become petrified  (It’s not because he’s not exactly ‘alive’ because Nearly Headless Nick wasn’t alive either, and he was petrified).

When Harry stabbed Riddle's diary the first time, ink splattered to the page next to it, but then it cut to a different angle and all of a sudden the second page was clean.  Then it cut again and you see the second page with a lot more ink than there was at the beginning.

When Harry is stabbed Tom Riddle's diary, the cut-scene where he closes the diary has his empty left hand closing it. In the scenes before and after, though, his left hand is raised and has the basilisk fang in it.

When Harry closes the diary to hit it with the Basilisk fang, there is a mistake regarding his wand.  After closing the diary, the shot goes back to Tom Riddle.  He is holding Harry's wand.  But then when Harry hits the book the first time and the shot goes to Tom, he is not holding the wand. After he hits it the second time he is holding it, and after the third time he is not.

As Harry stabs the diary with the basilisk fang, you can clearly see the dead basilisk behind him.  However, when Tom Riddle explodes into light and disappears you can see Harry and Ginny in front of him, and the basilisk disappears.  When the camera returns to a close up on Harry, the basilisk has returned to its original place again, dead, behind Harry.

When Harry plunges the basilisk fang into the diary, it's not in the center and it doesn't go very deep, but when Dumbledore shows the diary to Lucius it has a hole going through the entire diary in the center.

How exactly does the Chamber open up to the night sky? Fawkes, instead of taking them up a slide, takes them past a rocky cliff, right towards the moon and stars. And either everyone is blind, or they just haven't really searched for the Chamber of Secrets? "Oh, that's just a cliff and a statue of Salazar, nothing to see here..." (see False Mistakes and Why)

Harry didn't brush his teeth before he went to bed. It's clearly night time when they're pulled out of the chamber, and it's bright sunny afternoon daylight coming through the window to Dumbledore's office in the next scene, and Harry's still as dirty as ever. The famous Harry Potter is, after all, too good to take a bath I suppose...

At the end of the movie with Lucius in Dumbledore's office, the sun reveals Jason Isaac's (Lucius's) true short brown hair, underneath the blonde wig.

When Harry, Dumbledore, and Lucius Malfoy are in Dumbledore's office and Harry says he will be always be around to save the day, his face is clean. Later, when Harry gives Lucius the diary, his face is as dirty as it was when he was in the Chamber.

Percy and Penelope sure do get around a lot. At the end, they're walking towards the Ravenclaw table and then they're walking past the Slytherin table.

When Hagrid enters the Great Hall, the next scene shows the doors closed. Then soon after they're open again when nobody came in.

During filming of CoS, Emma Watson broke her wrist. Several times during the movie you can see a little bit of her cast showing.