Pretty much everyone, if you're re-reading after having finished the series. Particularly Snape, Dumbledore, Scabbers, and Aunt Petunia.
After The Reveal about her in Book 5, was Mrs. Figg letting Harry have some joy while being babysat by her after she broke her leg due to the injury? Or could she just not take having to mistreat him any longer and let her façade crack?
Did McGonagall know Hermione was fibbing about why she, Harry, and Ron were in the bathroom with the troll? If so, did she let it slide because she was mostly just glad they were alive? Because she was glad that Hermione had finally made some friends? Or because she figured fighting the troll was punishment enough?
Speaking of the troll incident, what was Hermione's reason for lying in the first place? Was it because she was embarrassed and didn't want to admit that she'd been crying, was it to forgive Ron and have him evade punishment, or was it both?
It's said that Quirrell was as timid during his childhood as he is appeared to be until the final confrontation. But was the more confident persona he presented at the end his own (from years of Voldemort's tutoring), or was it a side effect from having Voldemort "attached" to him?
Complete Monster: The evilest character in the series makes his debut here (see this page for details).
Epileptic Trees: The very first UK edition had on its back cover an illustration of an adult wizard who didn't match up to any of the main adult characters. He was later replaced by the same artist with an illustration that's clearly of Dumbledore. Fans thus wondered who this wizard could be, with some thinking he could be Nicolas Flamel (due to having a bulge in his pocket, thus the titular Stone), or else Dumbledore but erroneously drawn much younger. The illustrator confirmed years later that he just intended to draw a random wizard, based on his own father.
Rereading the opening of this book with Dumbledore telling McGonagall about how little they have had to celebrate for eleven years... and with the knowledge of how bad things were under Voldemort was when he was in charge in Deathly Hallows...
Harry's thoughts about the Dursleys taking all of his Gringotts money had they known about it becomes this with the reveal that one of the reasons Uncle Vernon started disliking wizards is that when Lily arranged a meeting between their families, Vernon took the tales of James's usual wizard routine (like moving around in flying brooms as opposed to cars) as wizards living off government help, just to have James casually tell him that his family is in general quite rich and goes as far as to explain wizard currency (which involves ACTUAL gold and silver coins) and mention his own (later Harry's) Gringotts vault. To make it worse, James wasn't even trying to be malicious about it but Vernon still took it badly...
Dumbledore's warning to Harry about how wizards have wasted away before the Mirror of Erised and its depictions of their deepest desires takes on a darker personal note when Fantastic Beasts: The Crimes of Grindelwald reveals that Dumbledore himself would stand before the Mirror and pine away for Grindelwald.
One moment that could be this or (even more) Hilarious in Hindsight is the passage in the Christmas chapter describing the Weasley Twins enchanting snowballs to bounce off the back of Professor Quirell's turban after you've read the end of the book and discovered what he's keeping under there. This arguably sails into Harsher in Hindsight after Deathly Hallows has Voldemort get some payback.
Percy Weasley telling Harry at the Start-of-Term Feast that Dumbledore is a genius, but "a bit mad" becomes this by the fifth book, when Percy is loyal to the Ministry of Magic that's trying to make Dumbledore look like a power-hungry loon.
Dumbledore, when asked by Harry about what he sees in the Mirror of Erised, amusingly replies that he sees himself holding a new pair of socks. Word of God after the seventh book has confirmed that he was lying; what he actually sees is his dead sister Ariana alive and well, and his estranged brother Aberforth having forgiven him.
Harry magically freeing the boa constrictor at the zoo and setting it on Dudley is funny, until you read the next book and realize Harry, unintentionally, did the same thing as Tom Riddle when the latter first opened the Chamber of Secrets. Only the fact that the snake was more interested in escaping prevented something far worse from happening.
Sending the students to their dormitories because there is a troll in the dungeon. Turns out that's where the Slytherin Common Room is.
Harry talking to the snake at the zoo after accidentally freeing it is treated as another whimsical magical event. Turns out how Harry got this ability and its historical usage is anything but whimsical.
Heartwarming in Hindsight: Dumbledore awarding Neville points for standing up to his friends might seem like an Ass Pull to ensure Gryffindor wins the House Cup, but then we later find out that Dumbledore was in love with Gellert Grindelwald in his youth, and was hesitant to fight him because of it. He was basically awarding Neville for something he himself didn't have the courage to do until it was too late.
Fred and George's winter prank on Quirrell becomes much funnier after the reveal at the end.
Hermione and Ron's initial animosity becomes this as people continue to read the series and it becomes blatantly clear that they're the Official Couple.
After making a small gag about King's Cross having a mystical Platform 9¾, the actual King's Cross Station was given an unusually numbered platform, Platform 0, in 2010.
The publisher changed the name to Harry Potter and the Sorcerer's Stone because of concerns that children would find an artifact associated with philosophers boring. Now, thanks to popular works of fiction like Devil May Cry and Fullmetal Alchemist, many young adults know what a "philosopher's stone" is.
The book's line that Quidditch referees "had been known to vanish and turn up months later in the Sahara Desert" gets a little meta boost when you consider that Madam Hooch, the Hogwarts Quidditch referee, disappeared after the first movie. Of course, she did continue to appear in the books, but still.
It Was His Sled: Snape is a Red Herring, the teacher trying to kill Harry is Professor Quirrell, and he is hosting Lord Voldemort inside his own body.
Memetic Troll: Dumbledore on account of waiting until the very last minute to give Gryffindor just enough points to beat Slytherin.
Ship-to-Ship Combat: Probably few people realized just how big and vicious a battle this book would begin among its fans, most prominently among Harry/Hermione and Ron/Hermione shippers.
Signature Scene: Harry seeing his deceased parents for the first time in the Mirror of Erised, one of the series' biggest tear jerkers.
Slow-Paced Beginning: Notably, it takes about a third of the novel before Harry gets to Hogwarts. And quite a few children readers were turned off by the first few chapters for being too slow-paced; not to mention most of Rowling's dry satire on middle-class insecurities flying straight over their heads. The film, incidentally, pares this down somewhat, with the pre-Hogwarts section of the story reduced from covering a third of the book to a fourth of the movie. And in the video game, the pre-Hogwarts events are sped over in a quick slideshow.
Squick: Dumbledore's experience with the Every Flavor Beans. He lost his liking to them a long time ago because of a vomit-flavored one, and when we see him actually try another, it's earwax-flavored. If that isn't disgusting enough, George Weasley claimed to have eaten a booger-flavored bean.
They Wasted a Perfectly Good Plot: Many have pointed out the oddity in Philosopher's Stone that despite being a story centered around a Wizarding School, the main character goes the whole book/movie without ever casting a single spell with his wand. As a result, other than turning out to be a good flyer on a broomstick, you never get to see how Harry grew as a wizard during his 1st year at Hogwarts.
While the Slytherin house are meant to be Asshole Victims, Dumbledore bait-and-switching their House Cup celebrations by giving Gryffindor enough points to win - for ostensibly rule breaking, at that - at the absolute last minute can come across as surprisingly mean spirited.
Malfoy's first interaction with Harry and Ron can come off as this. This is Draco's big Establishing Character Moment, marking him as the stuck-up, mean, Spoiled Brat that he is, but Ron did invite a reprisal by rudely snickering at his name after Malfoy introduced himself to Harry. On the other hand, when Malfoy had already met Harry, he'd been incredibly rude about Hagrid and unintentionally insulted Harry's dead mother, and making fun of Ron's family and appearance was Disproportionate Retribution to say the least.
While Malfoy's scene is debatable, Dudley receiving a pig's tail in the book is nothing short of Unintentionally Sympathetic, especially since Hagrid said he was actually trying to turn him into a pig. In that scene, Dudley hadn't even done anything- it was Vernon who insulted Dumbledore. The film averts this by having Dudley eat Harry's cake, though even that comes across as Disproportionate Retribution.
Dumbledore's final altering of Gryffindor's points. While the house's students did pull off quite a heroic feat and are worthy of the points, it still comes across as a huge dick move to only award them these points after you've just announced Slytherin has won, and then proceed to take away their victory.
Values Dissonance: Vernon Dursley's acquisition of a rifle (a shotgun in the movie) to protect his family while at the Hut-on-the-Rock is more alarming from a British perspective due to the more strongly regulated firearm ownership in the UK. Rifles and shotguns can be owned by British citizens with a certificate provided that the firearm in question meets certain specifications. However, gun ownership explicitly for personal protection has been banned since 1938, and use of a firearm in a self defence situation is generally illegal. Petunia, Dudley, and Harry are all shocked when Vernon reveals the rifle to them.
The Woobie: Harry is this at the beginning for living with family members who are abusive towards him.
The film
Franchise Original Sin: The film's changing Ron keeping a cool head in the Devil's Snare to Hermione keeping a cool head while Ron panics uselessly isn't so bad on its own — Ron gets his chance to shine in the chess match later — but it marked a disturbing trend in later films where Ron's moments of courage and intelligence were changed to Hermione or Harry's moments of courage and intelligence, while Ron ended up more the comic relief.
Genius Bonus: The chess endgame is designed so that checkmate could be achieved by sacrificing either Harry or Ron, which adds some extra pathos to Ron's decision to sacrifice himself. Also, avid chess players may recognize Ron's opening move as the Scandinavian Defense, in which White taking the early pawn is entirely expected. Doing this lets the trio check what's going to happen when White captures while leaving them with a perfectly playable position. For bonus points, the Scandinavian allows Ron to more easily deploy the queen so that he can keep the three of them relatively safe (note that at the end of the game, the black queen is gone but most of the other non-pawn pieces are intact until Ron sacrifices a rook and himself to set up the checkmate).
One-Scene Wonder: As expected with this franchise, but the literal examples are John Hurt as Ollivander and John Cleese as Nearly Headless Nick.
Out of the Ghetto: As with its literary counterpart, Harry Potter and the Philsopher's Stone broke through with a kid-skewing fantasy story that managed to pull in audiences of all ages and genders. Before then, fantasy films centred around and aimed at children typically had low budgets, indistinguished casts aside from maybe a notable actor or two who wanted a new house, and seldom had a story and world comparable to more higher-age fare. Warner Bros. was so skittish over the idea of the film falling into the ghetto that they bandied around ideas to make it palatable for American audiences, from moving the film to the U.S., aging up the characters into teenagers, making it an animated film, or making sure there was a reputable name behind the camera (Steven Spielberg emerging as a strong candidate) and in front (recent Oscar nominee Haley Joel Osment was a highly rumored name for an Americanized version). J.K. Rowling, however, vetoed their ideas and strongly insisted the film stay true to the source and its British roots. As a result, WB threw all its weight behind that focus, spending blockbuster resources, grabbing cutting-edge effects houses, a laundry list of British acting legends (the main child characters, though, would be largely unknowns), legendary composer John Williams, and highly successful director Chris Columbus. Hewing close to the beloved novel and marketed with an all-out blitz, the film was a massive success, scoring the biggest opening weekend of all time and finishing with the second-highest worldwide gross ever, even beating fellow ghetto-busting fantasy The Fellowship of the Ring at the money till. This opened a wave of more fantasy and YA adaptations with more resources behind it, as well as kicking off one of the most profitable series in cinematic history.
Julianne Hough and Derek Hough both appear in the movie as background Hogwarts students. Although American, they were living in Britain at the time, and the students at their performing arts school were recruited as extras for the film. Julianne is the blonde girl next to Dean Thomas during the Quidditch match. Derek is the Ravenclaw boy walking behind Hermione when she's preparing to leave for Christmas.
Just prior to her leading role on The Story of Tracy Beaker, Dani Harmer appears in this film as a background Hogwarts student. She's the girl seated next to Oliver Wood in the shot that appears after Hermione exclaims, "We're tied with Slytherin!"
Special Effects Failure: On the whole, the effects in this film are some of the weakest throughout the series, and served as the only film to use either Sony Pictures Imageworks, Rhythm & Hues or Jim Henson's Creature Shop (all of whom were going through slumps at the time, combined with the rush to get the effects done). More specific examples include:
The Mountain Troll scene. It's incredibly obvious that a CGI double was used for most of the shots where Harry was clinging to the Troll's body.
Only one of the shots of Scabbers in the train scene uses a real rat; the others use a puppet with very mechanical-looking movements.
The Quidditch match is home to a lot of obvious green screen compositing and digital doubles.
Contested Prequel: The sixth-generation games are either disliked for being heavily recycled from the previous year's Chamber of Secrets game on the same systems, or appreciated for being a step up from the previous PC and PS1 games in most aspects. Flandrew's review comparing the five games sums up both arguments pretty well.
Goddamned Bats: Gnomes in the PC version are annoyingly fast, hard to dodge, and steal your beans if they hit you. They also have high-pitched, unnervingly human voices. Thankfully, they were toned down in the sequel, where they can actually be useful by turning Horklumps into beans.
Goddamned Boss: The fight against Quirrell's Gytrashes in the next-gen version. The boss is just like any fight against Gytrashes earlier in the game except they can spit out projectiles at you, are plentiful and very resilient. Even worse, every once in a while, Quirrell will resurrect one which you can thankfully stop by throwing a flipendo at him. Unfortunately, with everything that's going on, you could be way too late to stop him, making the fight drag on longer than it's supposed to be.
So Bad, It's Good: The voice acting, especially the Finnish dub of the PC and PS1 version. The latter gets a special mention due Dumbledore's voice changing randomly from a old man voice into a sinister voice.
Special Effect Failure: If you look closely at some of the fountains in the greenhouse in the PC version, you'll see that the water streams are flowing upwards instead of downwards.
The GBC version of the Mountain Troll fight, particularly for the unprepared. Not only does it hit harder than anything you've seen before and have a suitably large amount of health, but the method Ron used to clobber it in the book doesn't work. And it's part of a sudden Plot Tunnel, with no way to level grind or prepare in other ways after you've entered it.
Chasing Malfoy in the PC version, mainly because the game doesn't bother to tell that you actually have to go fastest speed to damage Malfoy. The PS1 version at least shows you have to press the Square button to damage him.
PS1 has a minigame where you chase a peacock so that you get three feathers from it. Frustating part is that there is a time limit and the peacock is quite fast.
That One Sidequest: In the PS1 version, getting the Wizard Cards in Gringotts is particularly tricky. Specifically, you have to complete the already somewhat tricky mine cart minigame, while also collecting every bonus gem. Miss one gem, and the entire minigame needs to be repeated, and that’s without mentioning that missing a single coin on the strings that reveal gems will cause the gems to not spawn. The amount of precision needed to successfully grab every gem in looping patterns is a fair bit higher than what the game usually demands. Also, if you complete the coin collecting, but don’t get the gems, while you are given the choice to try again for the gems, if you leave, the vault will lock, and you won’t have another chance at going for the Wizard Card.
Underused Game Mechanic: In the PS1 game, the last two spells you learn end up this way. Defence Against The Dark Arts teaches Verdimillious, a spell that makes transparent platforms become solid for a short time. After using it in the class, there is one other set of platforms in the entire game, which happen to be in the next room you’re intended to go to. After crossing those platforms and entering the next area, the spell goes unused for the remainder of the game. Avifors, from the Transfiguration class, fares slightly better, in that there are two statues to cast the spell on after the class, but again, these are both in the very next rooms you’re intended to go to, and are locked into, and once they’re both sorted, the spell goes unused for the rest of the game.
who didn't match up to any of the main adult characters. He was later replaced by the same artist with an illustration that's clearly of Dumbledore.
