Hogwarts Security System

Hagrid states that Hogwarts is one of the safest places to keep something hidden, as in the Sorcerer's Stone. However, three first years were able to make it through the "traps" to get to the last set up. How safe could Hogwarts be if that were possible? A Fidelius Charm would have been easier to keep the Stone safe!

Elusive Woman

JKR said in an interview that the Ravenclaw Ghost, the Grey Lady, can actually be found roaming the halls in the first book. The HP Lexicon informs us that in the American Hardcover edition, page 210, JKR writes: "They passed the ghost of a tall witch gliding in the opposite direction, but saw no one else." We believe that this is the Grey Lady!

Immortal, but not really

Dumbledore said that Nicholas Flamel will die as soon as he sets his affairs in order. How can he, if the Stone makes him immortal? If it means that he could only stay alive by drinking the elixir, then he isn't really immortal at all!

It’s a Small World

In the beginning of the book, Hagrid mentions that he borrowed the Motorcycle he used to fly across England from Sirius Black, who we find out is Harry's godfather in Prisoner of Azkaban.

Book Two – Chamber of Secrets

Birthday Baffles

We've discovered Harry's official birthday! We know that he was born on July 31st and since Nearly-Headless Nick's death-day party in the Prisoner of Azkaban was in 1992, it means that Harry was 12 in 1992. If this is true, he must have been born in 1980! This brings up another mistake: In the Sorcerer’s Stone, Harry said his birthday was on a Tuesday. However, July 31st, 1991 took place on a Wednesday!
Thanks, MuggleNet!

Book Three – Prisoner of Azkaban

Trelawney’s Predictions

Trelawney predicted that Neville's grandmother would become ill...could this be part of a future book?

Who is the red-haired man Parvati Patil should look out for? Will this show up in future books? All of Trelawney's other predictions came true...

Teacup Truths

When Harry is reading Ron's cup in Divination, he sees "Trials and Suffering" and then "Great Happiness". This was a hint as to the outcome of Buckbeak's trial!

Crookshanks is…

Crookshanks isn't an ordinary cat. He's part kneazle, for those who haven't read Fantastic Beasts and Where to Find Them.

Book Four – Goblet of Fire

Barty’s Trials

In chapter thirty-five of the Goblet of Fire, Barty Crouch Jr. tells how he worked so hard to make sure Harry won the Triwizard Tournament and touched the Cup, which acted as a portkey. If all Barty needed Harry to do was touch a portkey, he could have made anything, Harry's wand or a book, for example, a portkey to Voldemort. Why go through all that trouble when it could be accomplished in a much easier fashion?

MuggleNet Adds:
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?

Editorial note on the above:
Of course one can argue that the whole point of guiding Harry through the Tri-Wizard tournament is to be able to keep Voldemorts return secret. No one would have been able to see what would happen if Harry had touched the cup, was transported to revive Voldemort, and after that send back to Hogwarts, dead. He'd have turned up in the maze dead and it wouldn't have made anyone suspicious of Voldemorts return, whereas Harry disappearing out of the Hogwarts grounds is highly suspicious. In addition to all that, yes, portkeys do work on the Hogwarts grounds, apparating and disapparating however, does not.

The Not-So-Secret Secret

At the end of , Hagrid mentions that he and Madame Maxime are going to do something that summer that Harry couldn't know. Well, it's it obvious that they went to try to persuade the giants to come to the good side! Dumbledore had suggested this to Fudge earlier in the book.
Thanks Gallexia

Mundungus Backstabber

In chapter three of the Chamber of Secrets, Mr. Weasley comes home and says that Mundungus Fletcher tried to put a hex on him while his back was turned. Then in the end of the Goblet of Fire when Dumbeldore is telling Black to round up the old crowd he mentions Mundungus Fletcher again, but why would someone working on Dumbledore's side want to put a hex on a Ministry of Magic member?
Thanks Leo