It is fair to say that J.K. Rowling's Harry Potter series is a masterpiece with her minute eye for detail and her ability to hold so many storylines together. However, even the biggest master cannot be flawless, and there are still a few mistakes or incongruences that sneaked their way into the books. I am aware that many websites already exist where all the tiny mistakes are laboriously collected; however, for this list I write the most noteworthy I encountered myself when reading through the books again.
I have already marked all the mistakes I found in Harry Potter and the Philosopher's Stone and you can find the blog post here. This blog post is about the second of the HP books, and if you found other mistakes that are not listed here, just drop me a message here or on social media.
First off a really obvious mistake that bears a few problems with it and really should have been avoided, considering what happens just a chapter later. In the very beginning of the book it says, "What did the Dursleys care if Harry lost his place on the House Quidditch team because he hadn't practised all summer?"
First of all, how on earth could Harry, even if he was from a wizard family, practise Quidditch in a muggle area like Privet Drive? It's not like you can fly around on a broom unseen very easily. Also, it is stated regularly - almost in every Harry Potter book - that underage wizards and witches must not perform magic at home. I daresay flying a broom would count to "using magic". This mistake is especially remarkable because Harry actually gets in trouble for "using magic" (even though it is actually Dobby) in THIS VERY BOOK. This must be a combination of Rowling's weaker moments and a poor editor who didn't realise how contradictory this is.
Our next stop leads us to the Burrow, the Weasleys' home. In the chapter The Burrow, Harry looks at all the things the Weasleys have in their house, among them a clock is described as, "The clock on the wall opposite him had only one hand and no numbers at all. Written around the edges were things like 'Time to make tea', 'Time to feed the chickens', and 'You're late'." The same clock is described very differently in Harry Potter and the Half-Blood Prince, namely as, "Harry recognised it at once: It had nine hands, each inscribed with with the name of a family member, and usually hung on the Weasleys' sitting room wall, though its current position suggested that Mrs Weasley had taken to carrying it around the house with her."
Now, first of all, the clocks are clearly not the same, and in the movie version they opted for the design of the second from book 6, rather than the one from the original book. Another discrepancy is that the clock hangs in the kitchen in book 2, but in book 6 it is stated it usually hangs in the sitting room wall, so that doesn't go well together either. Of course they may have two different clocks, but why would Harry then recognise it? Very mysterious...
For the next weird occurrence, there may be an explanation, but it is still quite odd. Harry consistently hears voices no one else can hear. Later we find out that's because he's a Parselmouth and the snake speaks in snake language, too. However, Ron remarks in the Duelling Club chapter that they heard Harry hiss when he spoke in snake language. Should Ron and Hermione then not at least hear hissing sounds from the walls? Surely, the Basilisk may have whispered, but does being a Parselmouth also mean you have super hearing and can hear better than non-Parselmouths? If so, it's a pity Harry lost the ability after Voldemort's death...
Checking dates doesn't seem to be Rowling's strong suit. Already in the first book, the dates didn't check out, and it is the same in Book 2. In the chapter The Very Secret Diary, Hogwarts celebrates Valentine's Day and Lockhart sends kitschy Cupids to deliver Valentine's greetings, which leads to one of the most cringeworthy moments for Harry in the entire series. However, Book 2 takes place in the year 1993, and Valentine's Day this year was actually on a Sunday. I would also not like teachers like Lockhart who make me go to school on my well-deserved weekend...
Lastly, there is a mistake concerning Hagrid. In the chapter The Heir of Slytherin, Riddle tells Harry the story about the chamber and how Hagrid got kicked out for his mistake, he says, "On the one hand, Tom Riddle, poor but brilliant, parentless but so brave, school prefect, model student...on the other hand, big, blundering Hagrid, in trouble every other week, trying to raise werewolf cubs under his bed...".
Considering that Remus Lupin, the werewolf, appears only a book later, it is odd why Rowling would write this example in the book. There is no such thing as "werewolf cubs". Werewolves are humans who were bitten by another werewolf and subsequently have to transform into a monster each month at the full moon. Therefore, if Hagrid raised "werewolf cubs under his bed", he, in fact, had little cursed children stuffed under his bed and definitely deserves to be kicked out of school for that. Any other creature would have definitely made more sense.
Did you find these mistakes, too? Let me know if you found others that I missed...I am sure there's plenty more to find.