Extracted from Mugglenet.com
This could be old stuff.....but thought it was interesting to read.
Sorting Hat Stool - In SS, a four-legged stool is used for the sorting, but in PoA and GoF, it is a three-legged stool. Oh, and in OotP, it is just a 'stool'.
Long Fingers - Voldemort, Dumbledore, Snape, Mr. Ollivander, Sibyll Trelawney, Dobby and Goblins are all frequently described as having long fingers (Voldemort's are described as "unnaturally" long). Could long fingers be a sign of magical power?
Cat Lovers - Argus Filch, Arabella Figg: both have the same initials, both are squibs, and both love cats!
Wide-Mouthed Tree Frog - We've known ever since Sorcerer's (Philosopher's) Stone that Harry was going to be replaced as Seeker! At the beginning of the chapter right after Harry catches the Snitch in his mouth, Draco is making fun of Harry and saying how a "wide-mouthed tree frog is going to replace Harry as Seeker" next. This didn't exactly come true, but in Order, Umbridge (the wide-mouthed tree frog, check all the toad references about her) bans him from the team, essentially replacing him with Ginny!
The Marauders - James, Sirius, and Remus, all end in 'S', are loyal members of the Marauders and would never betray the group. Peter, who's name ends in an 'R', betrayed the Marauders by giving away James' secret and then let Sirius be wrongfully sent to Azkaban.
And here's another Marauder thought: Moony, Wormtail, Padfoot and Prongs aka Lupin, Pettigrew, Black and Potter, the best friends who invented the Marauders Map, listed their names in no particular order. But, first Prongs (James) dies, then Padfoot (Sirius)...could Wormtail be next?
How Old? - In the "enormous, old" reference book where Flamel is mentioned, it says that he was 665 years old as of "last year." That means he was the big 666 when the book was published.
Number, Please - In Order of the Phoenix, the phone number to get into the Ministry of Magic is 6-2-4-4-2 (which spells out "MAGIC").
'711' - The seemingly random number of Sirius's vault, 711 (which appears on page 315 in the British copy of the Prisoner of Azkaban) is also the number of the page in which Sirius falls through the veil in the British version of the Order of the Phoenix.
Tests - Harry seems to take his finals only every other year. He took them his first year, Dumbledore cancelled them for the whole school for the second year, he took them his third year, as a Tri-Wizard champion, he was exempt his fourth year, and then he took O.W.L.S. his fifth year.
Dursley Post - Harry receives a few Christmas packages from the Dursleys at Hogwarts. How do the Dursleys send Harry the packages? They refuse to have anything to do with magic and they hate owls ... Maybe through Dumbledore? And since they normally don't give Harry presents at Privet Drive, do they send the packages (such as they are) because Dumbledore SUGGESTS they do it?
Mirror, Mirror - There are instances where mirrors talk. In chapter four of CoS, a mirror at the Burrow tells Harry to 'tuck your shirt in, scruffy!' And in chapter four of PoA (another chapter 4!) ... "I'm not going to be murdered" Harry said aloud. "That's the spirit dear," said his MIRROR sleepily. Bring to mind a certain two-way mirror Sirius gave Harry in OotP? Maybe it will be useful after all...
Red and Green - There are quite a few references to red and green ... Gryffindor-red, Slytherin-green; Ron's maroon (red) Weasley sweater and Harry's green one; Dobby Christmas gift to Harry, a pair of socks - one red, with broomsticks, the other green with Snitches; in the forbidden forest, Harry and Draco are told by Hagrid to send green sparks up in the air if they found the unicorn, red sparks if they are in danger; Voldemort's eyes are red; Harry's eyes are green; Lily was a redhead with green eyes; The Irish National Quidditch team wore green robes, Bulgaria wore red; Voldemort's green killing curse and Harry's red Disarming Spell which collide when they dueled.
Blue Candles - The candles on the walls of Nearly Headless Nick's Death day party burn an unusual color--blue! Blue-burning candles are also found on the walls of the large, circular, spinning room in the Department of Mysteries. In SS, Hermione conjures blue fire and scoops it into a jar. The Goblet of Fire burns with a blue-white flame.
And speaking of odd color fire ... Harry and Hermione encounter purple and black fire in Snape's spell to protect the Sorcerer's Stone.
Knock, Knock - Dumbledore's office door has a Griffon doorknocker - 'Gryffin-Door', get it??? (sorry). Possibly this could have been Godric Gryffindor's office?
Rats! - Dudley's friend, Piers Polkiss, shares his initials with Peter Pettigrew. Both are likened to rats. Piers is described as "a scrawny boy with a face like a rat" and Peter, an Animagus with the ability to turn into a rat, also had "something of the rat linger[ing] around his pointed nose and his very small, watery eyes."
Cat-Dung - In OotP, Mundungus Fletcher is described as having "short bandy legs" and "long, straggly ginger hair" while Crookshanks is described as a "bandy-legged ginger cat." In POA, Crookshanks hair is described as "long". JKR has told us Crookshanks is not an Animagus, but is this only a coincidence?
Out of the Mouth of Ron - In CoS, Harry says, "I wouldn't mind knowing how Riddle got an award for special services to Hogwarts either". Ron says jokingly, "Could've been anything ... maybe he murdered Myrtle; that would've done everyone a favor...." He DID murder Myrtle, through the Basilisk.
Serpent got your Tongue - The Basilisk comes out of the mouth of the statue of Salazar Slytherin in the Chamber of Secrets, and the Dark Mark is a serpent coming out of the mouth of a skull. Hmmmmm, do you think they might be related??
Sirius' Knife - In POA, Sirius Black slashed that Fat Lady's picture with a knife. Later, he stood over Ron "holding a knife." Could this be the same knife that Sirius gives Harry as a present in OotP?
Doubles - Several characters have repeating initials... BB (Bellatrix Black), CC (Cho Chang and Colin Creevey), DD (Dudley Dursley, Dedalus Diggle, Dilys Derwent), FF (Filius Flitwick), GG (Godric Gryffindor and Gregory Goyle), HH (Helga Hufflepuff), LL (Luna Lovegood), MM (Minerva McGonagall, Mad-Eye Moody), PP (Peter Pettigrew, Piers Polkiss, Pansy Parkinson, Parvati and Padma Patil, Madam 'Poppy' Pomfrey), RR (Rowena Ravenclaw), SS (Severus Snape, Salazar Slytherin, Stan Shunpike) and I think we could throw in the Bloody Baron, Moaning Myrtle, Bertie Botts, and Peeves the Poltergeist.
Detention with Dolores - 'Dolores' means 'pain' in Spanish.
Don't Touch Me - In the UK editions of the HP books, there is the Hogwarts' coat of arms of the four houses surrounding an "H". If you look closely you can see that all the house mascots are touching some part of the "H" EXCEPT for Slytherin's serpent.
Silver Bullet - In GoF, Peter Pettigrew gets a nice, new, shiny silver hand. Now, we wonder what might happen if he crosses paths with a certain werewolf out for a night time stroll?
Went to Pieces - Voldemort's soul is probably in 7 pieces and there are seven books. What if one piece were hidden in each book?
Prediction Puzzle - MuggleNet has received several versions of the following coincidences about Ron and Harry's predictions, so we'll post one here that mostly summarizes what we've been receiving - make of it what you will!
In GoF, Ron and Harry sit making up predictions for Trelawney's class. If you read the book enough times, you start to realize that the predictions are more like foreshadowings. Ron suggests to Harry that he should write down that Harry gets stabbed in the back by someone he thought was a friend. That comes true when Ron gets mad at Harry for becoming a champion. Then Ron says that he'll come off worse in a fight. Later, Hermione and Ron fight about the Yule Ball and Harry thought that Hermione had gotten the point much better than Ron had. Harry said that Ron would lose a treasured possession and the gold he gave to Harry for the Omnioculars disappeared. Later Hermione came up after Harry and Ron were finishing their predictions and observes that Ron seems to be drowning twice. For the second Tri-Wizard task, Ron and Hermione are placed on the bottom of lake and Harry thinks they'll drown if he doesn't get them out.