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

Also, when Harry is talking to Dobby, if you look carefully, you can see the green ball on a stick, used to guide Daniel Radcliffe for talking to the computer-animated Dobby, in the reflection of his glasses. -- Thanks to Walter for this one.

When Dobby explains to Harry why he hid his letters, you can see the dresser drawers 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, if you look closely, you see all the drawers are slightly and unevenly open.

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

When Ron is beside the window, we can hear his voice clearly, even though the window is closed. Shouldn't it be muffled? -- Thanks to Greta for this one.

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

Also, when Ron, Fred, and George are rescuing Harry, the bars are sealed to the wall but when the bars are pulled off, the window is broken.  They weren't attached to the window. -- Thanks to Greta for this one.

In the first movie, Harry gets a Nimbus Two Thousand, which also appears in CoS when he's playing Quidditch.  So why is it that Harry doesn't put a broom in the Anglia on the way to the Burrow, isn't carrying a broom on his trolley en route to the platform, and the Anglia doesn't throw out a broom after the car is beaten up by the Whomping Willow?

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

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

When George, Fred, Ron and Harry return to the Burrow, look closely at the Weasley clock: You'll see that Molly's, Percy's and Ginny's hands are on garden.  Yet when we first see Percy and Ginny, they appear in their pajamas (Ginny coming from upstairs) as if they had just woken up.

When Harry arrives at the Weasleys' house, we see a shot of the fireplace he is going to travel through. There is no pot of Floo Powder or the 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 the camera 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, you'll see no sand slipping out; he simply crinkles his hand.  But in the next scene, he somehow has the sand, dropping it into the fire.

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 one hand, and you see her other hand at her side. Then there is a close-up of the can, and she is shown holding it with both hands.

When Harry slides out of 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, nothing like the dark and dingy surroundings that he walks out to in the ensuing shot.

Not only does Dobby block Platform nine and three quarters, but after impact and during a cut-scene, Hedwig's cage is closed despite having been blown open on impact.

When Harry falls out of the Anglia and is holding on to Ron, on a shot toward the end of the scene, packages suddenly appear behind the seat.  These magical packages also manage to not fall out of the car.

When Harry and Ron fly over the lake to Hogwarts in the Anglia, there is no reflection of the car on the lake.

When Ron's wand breaks in the car, you see him toss it into the back seat. When the Anglia chucks everyone and everything out, the wand is not shown being thrown out.  But Ron has his wand again later anyway.

When Harry and Ron land in the Whomping Willow, one shot from inside the car shows a branch coming through the rear window, then pulling right out again. In the next shot from outside the car, the branch is 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 gets 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 leaves no tracks: There are marks from the wheels only when it drives away on its own.

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

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

When the Anglia begins to drive off, its trunk is open.  You then see Ron and Harry running after it and when the shot turns back on the Anglia, the trunk is closed.

When Snape tells off Harry and Ron and shows them the Daily Prophet with the picture of the Anglia in the London sky, you can hear the car's engine. Magical pictures move, but they don't make sounds. -- Thanks to Béné for this one!

When Snape is talking to Harry and Ron about their driving the Anglia, Filch's arms are crossed and he's holding Mrs. Norris. When the scene changes, he is supporting her head with his right hand

The entire Herbology class should have fainted at the sound of the Mandrakes.  Seamus and Sprout have an entire conversation with the earmuffs.

When Errol delivers the Howler, landing on his back on the Gryffindor table, you can clearly see the Howler's seal is broken. Next scene shows Ron picking up the Howler -- which he has to break open. -- Thanks to Lesia for this.

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 knocks the books off the desk on purpose.

In the same scene, two of the pixies pull Neville up by his ears and hang him on a chandelier.  Because the pixies are computer-animated, the moviemakers had to put clips behind Neville’s ears to make it look like as though he were being lifted by the pixies.  After he is dropped onto the chandelier by the pixies, his ears are still stretched because of the clips.

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

The writing on the wall about the Chamber's having been opened was far above Harry’s and Filch’s head. So how did Ginny grow tall enough to write it?

In the Potions book with the Polyjuice Potion that Hermione shows Harry and Ron, if you look closely, you’ll see that on the bottom of the first 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 are they relevant to the Polyjuice?  You’re not supposed to use it to change into an animal.

During the scene in the Transfiguration classroom, the students' positions in the class are constantly changing. For example, in one shot, a blonde girl is sitting in the middle of the class next to a girl who looks, from the back, like Hermione. But in another shot, the girl is in a corner, and Neville has taken 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 backward (the film reel was flipped over for better picture") are what's there. This could also explain a later mistake regarding Harry's wand in his left hand.

When McGonagall is talking in her classroom about the Chamber of Secrets and she mentions that Salazar Slytherin wanted to admit only purebloods to Hogwarts, Hermione and Draco look at each other (meaning that Draco had to look completely the other way from McGonagall), but in the next cut Draco is looking at McGonagall.

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

When Harry is hit with the Bludger, it knocks off his arm guard, and leaves a sort of glove (that reaches his elbow), which is tucked into his sleeve. After Harry falls, the glove is over his sleeve; after Hermione destroys the Bludger, the glove suddenly (magically?) shortens, and you see only his sleeve where the rest of the glove sleeve was.

When Harry falls off his broom onto the sand, he is holding onto his broom with the arm the Bludger broke. -- Thanks to Brittney for this.

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

When Dobby visits Harry in the hospital, he bashes himself on the head with the Skele-Gro bottle, which Harry yanks from Dobby’s and puts on the table at the foot of the bed. After Dobby 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 disappeared, we see him jump on top of the covers. Half a moment later, the covers are over him. There is no way Harry can get under the covers three seconds after having landed on them.

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

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

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

When Crabbe and Goyle reach for the cakes Harry levitated, look at Ron and Harry in the background: It’s clearly not Ron. The double 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 the double 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. In the next shot, a wide shot, we see Harry’s shirt is buttoned up, nice and neat.

During the scene where Harry, Ron and Hermione have just taken the Polyjuice Potion, after Hermione and Ron run into the stalls, Harry is doubled over in the same sink where the potion cauldron was, and you see a distant shot of smoke rising from the cauldron. Seconds later,in a close shot on Harry, smoke is no longer rising. -- Thanks to Eloise for this!

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've just run through the puddle on the floor, their shoes are not wet.

In the scene in Hagrid's hut, a member of the crew can be seen on the shot. -- Thanks to Roza for this.

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 two feet from Harry and one second later, he’s right next to Harry.

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

When Harry, Ron and Lockhart are in the bathroom, having just discovered the entrance to the chamber, Ron asks Harry to say something in Parseltongue and there is a distance shot of this, with Ron looking at Harry. However, when the camera zooms in on the next shot, Ron is now looking at the sink. -- Thanks to Eloise for this!

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 as Harry approaches Ginny, he's carrying the wand in his left hand.  However, the wand, when thrown down, lands where his wand would have if it had been 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.)

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 stabs Riddle's diary the first time, ink splatters on the page next to it, but in the immediate cut to a different angle shows a suddenly clean page. Another quick cut, and you see the second page with a lot more ink than at the beginning.

When Harry stabs Tom Riddle's diary, the cut-scene where he closes the diary shows 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, who is holding Harry's wand. But when Harry stabs the book the first time, and the shot goes to Tom, he is not holding the wand. After Harry stabs the book the second time, he is holding it; after the third stab, 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 no Basilisk. When the camera returns to a close-up on Harry, the Basilisk has returned to its original place, 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 toward the moon and stars. So everyone is either 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 nighttime when everyone is pulled from the Chamber by Fawkes, and in Dumbledore's office in the next scene, it's clearly a bright, sunny afternoon (see the daylight coming through the window). But Harry's still as dirty as ever. Is the famous Harry Potter too good to take a bath?

In the scene where Lucius visits Dumbledore's office, the sun reveals Jason Isaacs'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.

At the end of the pixie scene when Harry, Hermione and Ron are left alone by Lockhart, the timing is off by a few seconds. Harry grabs for a pixie over his shoulder and throws it forward before the pixie is there. -- Thanks to Dodges.

When Malfoy calls Hermione a Mudblood for the first time, Harry reacts to the word as if he understands what it means -- but he later states he does not know what a Mudblood is (this can only be seen in the widescreen version -- Harry is cut out in the full-screen version. -- Thanks to Dodges.

When Harry is transforming into Goyle and he lets the Polyjuice Potion fall to the floor, his Slytherin tie is loose. When you see him again, his face transforming, the Slytherin tie he took from Goyle is neatly tied up nice and neat. Thanks to anonymous.

When Myrtle gets upset and dives into the toilet the water is supposed to splash out of the toilet bowl. Firstly she shouldn’t make a splash in the water. She can go through it. Ghosts can go through walls which are denser than water, but they splash on entering water? (Thanks to Tristan!)

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

In the scene after Hagrid enters the Great Hall, the doors are closed. Soon after, they're open again, even though nobody came in.

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

In the credits, Hannah Abbot is put down as "Hannah Hufflepuff." -- Thanks to Béné for this one!