The second Harry Potter book is much darker than the first. It introduces our first encounter with Voldemort of the past. We learn quite a bit about his history at Hogwarts as a teenager when he was known as Tom Marvolo Riddle.
This book also introduces us to the Chamber of Secrets and its dark and troublesome secrets within the castle walls. While both the book and film are favorites among many, there are some unresolved plot holes that have left us very curious over the years.
10 What made Dobby think Harry was going to be a target?
One of the big plotlines of the second book is that Dobby becomes convinced Harry is a target of the Chamber of Secrets and tries everything within his power to protect him. But how would Dobby have known that Harry was going to be targeted?
As far as we know, Tom Riddle doesn't even find out that Harry is attending Hogwarts until after he talks to Ginny Weasley. Harry isn't Muggleborn so he wouldn't have been a direct threat from the Chamber re-opening. It's still a little fuzzy exactly why Dobby was so determined to "save" Harry.
9 Why didn't the Horcrux in Harry die when he was pierced by the Basilisk fang?
During the final battle in Harry Potter and the Chamber of Secrets, Harry is actually attacked by the Basilisk. One of the fangs pierces his arm and he starts to die. Riddle is content to simply watch him die. But it's curious that the Basilisk venom does not extinguish the Horcrux inside of Harry since we later learn that Basilisk venom is one of the few things that can destroy a Horcrux.
J.K. Rowling did clear this up later on by stating the venom would have had to fully destroy the Horcrux as it did with the diary. Had Harry died from the wound, the Horcrux would have been destroyed.
8 Would the Basilisk actually fit in the pipes?
This is a question that has been a point of contention among the fandom for some time. In both the book and film, we know that the Basilisk travels around Hogwarts castle through the pipes. Hermione learns this after some diligent studying.
It is why Harry hears the mysterious whispering in Parseltongue throughout various corridors. However, by the end, we learn that Basilisks are more than 20 feet in length. Plus, when we actually see the creature, it becomes apparent that thing could not so easily fit through the pipes of the school.
7 How does Riddle know who the Muggle-borns are?
Once we learn that Tom Riddle is the one responsible for opening the Chamber of Secrets by using Ginny Weasley to do his bidding, one has to wonder how he knows who the school's Muggleborns are. He's been at rest for 50 years. It seems strange that he would know exactly which students to target at any given time.
Is there some way he is able to magically sense the blood status of those in the castle? He could have used Ginny to find out but how would she have known some of the more obscure students who she might have never even encountered before? It's not like she could go around asking people without attracting suspicion.
6 The Basilisk has strange eating habits
We've already established that the Basilisk was a monstrous creature. How on earth did it survive down in the chamber for years? Even if it was asleep during that time, once it awakened, it would have to feed on something.
It didn't eat any students at the school (that we know of anyway) so how did it get its constant stream of food? Also, the Basilisk is a giant snake. Why would there be bones left behind all over the place? Snakes don't spit out bones.
5 How did Ginny avoid getting caught in Harry's dormitory?
During one scene in the story, Ginny Weasley raids Harry's things for the diary after realizing he has come into its possession. How was she able to get into the boy's dormitory and basically destroy everything without being caught? We know that it isn't that difficult for girls to wander into the dormitories but surely she would have been making quite a ruckus up there considering everything was basically torn to pieces when the boys get back from class.
Even if the guys in that room were out, there likely would have been a few other Gryffindors around in the common room that would have seen Ginny leaving or entering in a frantic and panicked state.
4 Why didn't anyone ask Myrtle how she died?
When the Chamber of Secrets was opened for the first time, a student named Myrtle eventually died by the Basilisk. However, her ghost went on to haunt the girls bathroom ever since. She became known as Moaning Myrtle and all the students know about her, for the most part. She is one of many ghostly legends at the school.
Because of her ghost hanging around, you would think that one of the teachers or students would have considered asking Myrtle about how she died. Even if they hadn't thought to do so in the past, it's strange they wouldn't consider it in present. We know Myrtle has no issue talking about it.
3 Why didn't Ron's wand work but Hagrid's does?
Ron's wand gets snapped in half during he and Harry's excursion in the flying car. When they land in the Whomping Willow it wreaks havoc on the car and the two boys inside. Ron's wand is only kept together by a piece of spellotape and continues to malfunction throughout the entire book.
But why does Ron's wand stop wroking right when Hagrid only has pieces of his wand left and they seem to function just fine? Yes he has had a few incidences such as giving Dudley a tail, but for the most part he gets on fine with the pieces stowed away inside of his umbrella.
2 How did Lockhart get away with lying for so long?
Gilderoy Lockhart is a famous wizard due to the many incredible feats he has accomplished in the wizarding world. We're lead to believe that he has vanquished countless monsters, cured illnesses, and defeated dark wizards. Later we learn that Lockhart is a complete fraud and has merely been taking the credit for things accomplished by other wizards. He uses memory charms to ensure they don't remember anything about the encounters.
But what about the people that those wizards saved? Surely they would realize that Lockhart is not the actual wizard that rescued their town? Why didn't any of the witnesses ever come forward and give evidence that Lockhart wasn't who he claimed to be? One potential explanation is simply that Lockhart used places so far off the map no one would ever check. But still, he's made up a lot of lies, it's surprising none caught up to him.
1 How did Nick get un-petrified?
One of the side effects of encountering the Basilisk is petrification (or death). If you're lucky enough to only see the creature's stare through a reflective surface you'll merely be petrified instead of killed instantly. At one point, Nearly-Headless Nick, the Gryffindor ghost, gets petrified from seeing the stare.
Justin Finch-Fletchley gets petrified by seeing the stare through Nick. Human victims are eventually cured by a Mandrake Draught, but we never find out how Nick is cured. Obviously he cannot consume a Draught. Did he just eventually shake it off?