When Hagrid brought Harry to Diagon Alley for the first time, Harry heard a woman say "Seventeen sickles an ounce for Dragon Liver. They're mad." But Hagrid told Harry that there were seventeen sickles in a galleon. So that would be like saying "100 pennies" instead of a dollar.
When Hagrid comes and gets Harry out of the little hut on the rock, they use the boat that the Dursleys used to get to the rock. So how do the Dursleys get off the rock?
Harry buys the book "One Thousand Magical Herbs and Fungi", but later in the book it says Harry looked up 'dittany' in "One Hundred Magical Herbs and Fungi."
Petunia Dursley says that Lily would "...come home every vacation with her pockets full of frog spawn, turning teacups into rats...," but according to ministry rules, this is illegal. If she did this in her muggle home she would most likely be expelled as Harry almost was.
Just a thought but... security for the Sorceror's Stone could have been much better. If three first-years can get to the stone than you can bet any fully-trained wizard can do it. They could have just had a password that nobody but Dumbledore knew. Then he could tell Flamel if he had to use it than change the password right away.
In chapter 7, page 122, it says that Harry looked up at the Sorting Stool, there were only 3 people left to be sorted, Professor McGonagall calls the names of 4 more people instead.
'Ryan Richins' writes in to say: "In Book one (it said), Prof. McGonagall brings out a 4 legged chair with the sorting hat (to the sorting ceremony). In book four (it said) she brings out a 3 legged chair with the sorting hat. What happened to one of the legs?"
In Harry's letter from Hogwarts it says he could bring a cat, an owl, or a toad, but Ron still brings his rat, Scabbers.
In Book 1, JK Rowling wrote that Ron was the knight in the giant chess set. However, it later said that he had to 'move ahead one' so the Queen could take him, opening the path for Harry and Hermione to checkmate the king. If he was a knight, he could only move 1) ahead one, sideways two, or 2) ahead two, sideways one, like an "L".
In the first book it said that by drinking the Elixir of Life it would make the drinker immortal, but later in the story Dumbledore says to Harry that the Flamel's had enough Elixir stored in them to set their affairs straight.. But, if by drinking the Elixir of Life makes you immortal then you would never die, ever. You can't just be immortal as long as you have a certain item, then that would mean you could die. You would be like Achilles, you could still die. Immortal means you can NEVER die.
Book Two: Harry Potter and the Chamber of Secrets
At the end of the second book Dumbledore tells Harry that Lord Voldemort is the last remaining ancestor of Salazar Slytherin. But it should say that Lord Voldemort is the last remaining descendant of Salazar Slytherin.
When Tom Riddle was talking to Harry in the Chamber of Secrets he said that they were similar because they were both half bloods. But Harry isn't a half blood. Lily and James were both wizards and witches. (Many people say that because Lily was muggle born that makes Harry a half blood, but that is not true. If both parents are witches and wizards you are not a half blood. Half blood means ONE parent is a witch/wizard and the other is a muggle.)
At Nearly Headless Nick's Deathday Party, it said Peeves pelted Moaning Myrtle with peanuts, but he couldn't have, they would've just flown right through her, right?
When Harry goes back in Riddle's memory, Hagrid was expelled when Dumbledore wasn't headmaster -Professor Dippet was- but Hagrid said Dumbledore let him stay as gamekeeper at Hogwarts. (Perhaps Dumbledore let him stay on, even though he wasn't the headmaster, he was just a teacher).
The basilisk kills people by looking at it straight in the eye. But Myrtle and Harry both wear glasses. Colin was petrified by looking at it through the glass lense in his camera, so wouldn't Myrtle just be petrified too? The only other explanation is that maybe Myrtle had taken her glasses off to cry while she was in her stall.
Rose tells us: "In the first book, Nearly Headless Nick says that he hasn't eaten in "nearly four hundred years." But in the second book, he's celebrating his five-hundredth deathday."
Page 283 at the start of Chapter 16, very last word on the page is Professorr, it should be Professor, with only one R.
In the back of the paperback version of Harry Potter and the Chamber of Secrets, on the last page where it gives a preview of the next book, it reads: Harry Potter has to sneak back to his third year at Hogwarts after accidently inflating his horrible Aunt Petunia... I don't know maybe it only says that in my copy, but didn't Harry inflate his horrible Aunt Marge???
Book Three: Harry Potter and the Prisoner of Azkban
In Chapter 19, The Servant of Lord Voldemort, page 370, it states that Voldemort had been hiding for 15 years. If his power was lost only twelve years ago, why was he hiding that extra three years?
Remus Lupin recalls in his fifth year that OLD Madam Pomfrey used to walk him down to the Whomping Willow for him to transform. When Remus becomes a teacher almost 15 years later, Madam Pomfrey is still the nurse. Exactly HOW OLD is Madam Pomfrey?!?
In chapter 3, The Knight Bus, the driver Stan told Harry that the price to get to London was 11 sickles (an' fer firteen you get an...). But in the book it said Harry shoved some GOLD into Stan's hands. Sickles are SILVER, not gold.
In chapter 15, The Quidditch Final, it said Madam Hooch's whistle rang out as she soared over to Montague and began shouting at him. A minute later, Katie had put another penalty past the Slytherin SEEKER. It should say the Slytherin Keeper.
In book one, Marcus Flint is described as a burly sixth year, but in book three, two years later, he is still the captain and a chaser on the Slytherin quidditch team. He should have graduated in the last year. (JKR was asked about this in an online chat. Her response: "He had to do a year over again!" We can only assume this is an attempt to cover this minor mistake. We still love you JK!).
In book 3, Dumbledore says that he gave evidence at Sirius's trial, but in book four, Sirius tells Harry he didn't get a trial.
Book Four: Harry Potter and the Goblet of Fire
In Book 4, it states that it is the 422nd Annual Quidditch World Cup. In Quidditch Through The Ages, it states that the first World Cup took place in 1473. "Assuming my calculations are correct(Dumbledore)", that would mean the World Cup talked about in Book 4 takes place in 1895!
In book four, during Priori Incantatem, Voldemort's victims came out in reverse order. BUT, James came out BEFORE Lily. That would mean that James died AFTER he killed Lily and it said all over in the books that he killed James first. (Fixed in later versions of the book).
After Hermione dropped Muggle Studies, she said she had the same amount of subjects as Ron and Harry. But she still had (besides the mandatory ones) Arithmancy, Care of Magical Creatures, and Ancient Runes. Which is more then Harry and Ron who each had only Divination and Care of Magical Creatures.
When Dumbledore was telling everybody about the Triwizard Tournament during the start of term speech he said: "We have worked hard over the summer to ensure that this time, no champion will find himself or herself in mortal danger." (Don't you think facing a Hungarian Horntail that breathes fire forty feet would classify as 'mortal danger'? Even if there were trained hit wizards nearby you catch one of those flame-bursts and your a corpse before the wizards can do anything.)
When Harry recieved his letters from Hogwarts in Book one, it said they poured out of the fireplace. But in Book four the Weasleys were unable to get through the boarded up fireplace to pick up Harry as it was an electric fireplace. (Possible explanation: the fireplace was boarded up only after the letters started shooting down the chimney. Maybe Vernon Durlsey boarded it up so if it happened again, Harry couldn't get one.)
In book 2, it says that Moaning Myrtle haunts the U-BEND of the toilet. In book four, it says that she haunts the S-BEND of the toilet.
In Book four Fudge, Dumbledore, and Moody are talking ABOUT Crouch. But instead of Fudge yelling to Dumbledore, it says: "said Crouch angrily". He wasn't in the room... they were talking about him not with him.
Portkeys are supposed to transport whoever is touching the portkey at a prearranged time. But, Harry and Cedric were transported to Voldemort and the Death Eaters the SECOND they touched the Triwizard cup. Don't you think that sounds a little bit too... coincidental? Also, couldn't Moody/Crouch have just made Harry's pillow or something a portkey and transported him when he went to sleep at night? Wouldn't that have saved all the effort of guiding him through the whole Triwizrd tournament?
