Chekhovs Gun / Harry Potter

If the Chekhov's Armory in Harry Potter were an actual army, it would curbstomp everyone in a massive Zerg Rush. Also, there may be unmarked spoilers. Please list examples by book:

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    Harry Potter and the Philosopher's/Sorcerer's Stone 
  • An owl flutters past the window of Four Privet Drive on the morning after the night of Voldemort's defeat. As owls are soon revealed to be messengers for the magical community, this seems to subtly hint at the presence of a witch or wizard living in Little Whinging. In Order of the Phoenix, it is revealed that their neighbor, Mrs. Figg, is a squib.
  • Dumbledore appears "so suddenly and quietly you'd have though he'd just popped up out of the ground" and later disappears in the same way. Magical teleportation receives a proper name, Apparition, in the next book, and becomes an important method of transportation later in the series.
  • Dumbledore's nose is described as "crooked, looking as though it had been broken at least twice." We learn in Deathly Hallows that it was broken by his brother Aberforth at the funeral of their sister Ariana.
  • Dumbledore's "Put-Outer" next appears in a throwaway cameo in Order of the Phoenix before becoming critical to the plot about halfway through Deathly Hallows.
  • McGonagall complains about witches and wizards throwing caution to the winds in their celebrations, indirectly referencing the International Statute of Wizarding Secrecy which is named in Chamber of Secrets, is relevant to the plot early in Order of the Phoenix, and is critically important in the film Fantastic Beasts and Where to Find Them.
  • Dumbledore offers McGonagall a lemon drop. This is used as the password for his office in Chamber of Secrets.
  • Dumbledore mentions Madam Pomfrey complimenting his earmuffs. She appears later in the book as the school nurse.
  • McGonagall mentions Godric's Hollow, which is briefly mentioned in Half-Blood Prince before becoming a major location in Deathly Hallows, where we learn that it was named after Godric Gryffindor and that the Dumbledore family lived there for a time, and Cursed Child.
  • The circumstances behind Harry's survival and Voldemort's initial destruction are discussed, but they are not revealed until Half-Blood Prince and Deathly Hallows. Dumbledore remarks that "we can only guess," though Half-Blood Prince reveals that he, in fact, began extensive research on the subject.
  • Hagrid mentions borrowing the flying motorbike from Sirius Black. Sirius becomes a major character starting in Prisoner of Azkaban, while the bike itself reappears in Deathly Hallows.
  • Harry's scar initially seems to just be a scar. However, its importance increases significantly as the book and the series progresses.
  • Harry is left on the Dursleys' doorstep with nothing but a blanket and a letter. The letter is not referenced again until Order of the Phoenix and Half-Blood Prince, while the blanket is of major importance in Cursed Child, as it contains a hidden message from Harry's son Albus and his friend Scorpius Malfoy who are trapped in the past.
  • Petunia Dursley is established as an important character, though a reader may wonder why Dumbledore took Harry to live with his horrible, abusive relatives or why Harry in the later books even bothers to return to the Dursleys' home at the end of each school year. In Order of the Phoenix, it's revealed that because she has Lily's blood in her, her presence protects Harry from Voldemort until he comes of age.
  • Marjorie Dursley is mentioned several times. She makes an appearance in in Prisoner of Azkaban.
  • Mrs. Figg is a very minor character here and then does not appear again until Order of the Phoenix, where she is important early in the plot.
  • Harry discovers that he is able to communicate with a boa constrictor at the zoo. This ability, Parseltongue, is elaborated on in Chamber of Secrets and its origin in Harry is not explained until Deathly Hallows.
  • Harry remembers the flash of green light, which is not revealed to be the Killing Curse until Goblet of Fire. The fact that he has memories of when he was only one year old (and thus biologically unable to form memories) is indirectly explained in Deathly Hallows as actually being the memories of Voldemort's Horcrux.
  • Harry recalls being bowed to by a little man in a top hat, who is later revealed to be Dedalus Diggle. He does not become an important character until Order of the Phoenix.
  • Harry and the Dursleys stay at a hotel in Cokeworth. As revealed on Pottermore, this is where Petunia and Lily and Snape grew up, and the town reappears in Half-Blood Prince when Bellatrix and Narcissa visit Snape at Spinner's End.
  • Harry remembers being given a pair of Vernon's old socks for his tenth birthday. He later uses these to muffle his sneakoscope in Prisoner of Azkaban before giving them to Dobby for Christmas in Goblet of Fire.
  • Hagrid is repeatedly described as a "giant." In Goblet of Fire, it is revealed that he is literally half-Giant.
  • Harry's letter lists "Order of Merlin, First Class" as one of Dumbledore's titles. It is revealed in Deathly Hallows that this was awarded to him in 1945 for defeating Gellert Grindelwald.
  • Hagrid's dismissive attitude towards Muggles is a taste of anti-Muggle prejudice that is prominent later in the series.
  • Vernon mentions having promised to "stamp out" Harry's magic. It seems like an idle threat at the time, but come the Fantastic Beasts movie, we learn that, not only is this possible, it's incredibly dangerous to all involved. It's very lucky for Harry, the Dursleys, and the world that he did not become an Obscurial.
  • Hagrid mentions Voldemort's followers, who are not identified as Death Eaters until Goblet of Fire. He also vaguely describes the First Wizarding War, which is elaborated on significantly in Order of the Phoenix. Furthermore, Hagrid mentions the Bones and Prewett families, members of which later appear in the series (Molly Weasley and Susan Bones later in this book and Amelia Bones in Order of the Phoenix), and the McKinnons, all of whose deaths are elaborated on in Order of the Phoenix.
  • Hagrid speculates that Voldemort didn't have enough human left in him to die. Half-Blood Prince reveals that no, he didn't. He also adds that some believe he's still out there "somewhere," which, in Goblet of Fire, is revealed to be Albania.
  • Hagrid says that some of Voldemort's followers came out of trances, which is revealed to be caused by the Imperius Curse in Goblet of Fire.
  • Hagrid says that Hogwarts is "the finest school of witchcraft and wizardry in the world," implying that others exist. We learn about two others, Beauxbatons and Durmstrang, in Goblet of Fire, and the others (Ilvermorny, Koldovstoretz, Castelobruxo, Uagadou, and Mahoutokoro) were later revealed on Pottermore.
  • Hagrid says that he was expelled from Hogwarts in his third year. The circumstances behind this are explored in Chamber of Secrets.
  • Hagrid explains how secure Gringotts is, that dragons guard the high security vaults, and also how unwise it is to try double-crossing Goblins. All of this comes up again in Deathly Hallows.
  • Hagrid says that Dumbledore declined to become Minister for Magic, but the actual reason is not revealed until Deathly Hallows. He also mentions Cornelius Fudge, who appears in Chamber of Secrets and remains an important character until Half-Blood Prince.
  • Hagrid mentions that one reason for wizarding secrecy is that Muggles would want magical solutions to all of their problems. His answer was likely influenced by "The Wizard and the Hopping Pot," a fairy tale from The Tales of Beedle the Bard in which this is a major plot point.
  • Harry's course books include A History of Magic by Bathilda Bagshot, who is important in Deathly Hallows, and Fantastic Beasts and Where to Find Them by Newt Scamander, the protagonist of the five-movie prequel series. The latter text is also greatly expanded in the book of the same name
  • There is a used book store right next to the Leaky Cauldron on Charing Cross Road. Muggle detective Cormoran Strike visits this store in The Silkworm while investigating a murder.
  • Hagrid speculates on the reasons for Quirrell's twitchiness. Though the encounter that left him this way is later revealed to have been with Voldemort, the circumstances of this are not revealed until Goblet of Fire.
  • Hagrid and Harry pass Eeylops Owl Emporium, which includes snowy owls. One of these is Hedwig, who Hagrid buys for Harry later in the chapter.
  • Griphook, the goblin who shows Harry to his vault, reappears in Deathly Hallows with an important role.
  • Harry meets a boy at Madam Malkin's who is later revealed to be Draco Malfoy, a major character for the entire series. He mentions both of his parents, who also become important later in the series. His father, Lucius, first appears in Chamber of Secrets, and his mother, Narcissa, makes her debut in Goblet of Fire.
  • Harry finds a book at Flourish and Blotts that mentions the tongue-tying curse, which comes up again in Deathly Hallows to prevent Snape from revealing the location of 12 Grimmauld Place to the Death Eaters.
  • Mr. Ollivander later makes a cameo in Goblet of Fire before becoming an important character in Deathly Hallows.
  • Ollivander mentions that James Potter's wand was "excellent for transfiguration." In Prisoner of Azkaban, we learn that he was highly skilled at transfiguration, as he was able to become an Animagus.
  • The wand that chooses Harry has a phoenix feather core from the same phoenix that provided the feather for Voldemort's wand. Not only does the phoenix, Fawkes, appear in Chamber of Secrets, but the matching cores is a critical plot point from Goblet of Fire on.
  • Molly and Ginny Weasley both have minor roles here but go on to be important characters starting with Chamber of Secrets.
  • Ron mentions his mother having a second cousin who is an accountant. The existence of squibs is revealed in Chamber of Secrets.
  • Ron mentions his his father, Arthur, who becomes an important character from Chamber of Secrets on.
  • Scabbers is merely Ron's pathetic pet rat. In Prisoner of Azkaban, he becomes far more important when it is revealed that he is actually Peter Pettigrew.
  • The Trolley Witch makes her first appearance here and continues to be a minor character throughout the series until her full role and backstory are revealed in Cursed Child.
  • Dumbledore's Chocolate Frog card mentions both Gellert Grindelwald and Nicolas Flamel. The mention of Flamel is important later in the book, and Grindelwald is important in the backstory revealed in Deathly Hallows and is the villain of the prequel movies.
  • Nott is one of the students who is sorted, though his first name (Theodore) and house (Slytherin) are not revealed until his next appearance in Order of the Phoenix. He has another minor role in Half-Blood Prince before having an important role in the events leading up to Cursed Child.
  • Harry notices that Quirrell is wearing a purple turban that he was not wearing when they first met and shook hands. The reason for this turban is revealed at the end of the book.
  • Blaise Zabini is sorted into Slytherin and then does not appear again until Half-Blood Prince, where he has a minor role.
  • Seamus asks Nearly-Headless Nick how the Bloody Baron got covered in blood. The answer is revealed in Deathly Hallows.
  • The feast vanishes and is replaced by dessert. It is revealed in Goblet of Fire that this is done by Hogwarts' staff of House-Elves.
  • When Snape is introduced, he is looking directly at Harry. Not at his scar, but his eyes. The reason why is revealed in Deathly Hallows. Harry's scar begins hurting, but this is actually because Snape is explicitly looking past Quirrell's turban under which Voldemort is sensing Harry.
  • Percy explains that Snape knows a lot about the Dark Arts. We learn in Goblet of Fire that he used to be a Death Eater.
  • Snape is introduced here and is a major character, but here he's just the unpleasant Potions Master. His critical importance in the story continues to unfold across the rest of the series.
  • The Weasley twins are said to know more about the castle's secret passages than anyone. Prisoner of Azkaban reveals that this is because of the Marauders Map.
  • Professor Binns mentions Emeric the Evil and Uric the Oddball. They get a bit of expansion in Deathly Hallows and the Fantastic Beasts book, respectively.
  • Quirrell's excuse for his turban is that it was a gift from an African prince for getting rid of a zombie. Inferi are important in Half-Blood Prince.
  • The bezoar mentioned briefly in Harry's first Potions class is later used in Half-Blood Prince for Harry to circumvent an antidote challenge, and to save Ron after he accidentally drinks a bottle of poisoned mead.
  • Quidditch Through the Ages is mentioned several times and is greatly expanded in the book of the same name.
  • The trophy room makes a brief appearance here before becoming much more important in Chamber of Secrets.
  • The first years learn Wingardium Leviosa, the levitation charm, which comes in handy later in the book as well as the series.
  • Hermione's bluebell flames first appear with little importance but become very useful later in the chapter for distracting Snape and later in the book for repelling the Devil's Snare.
  • When the students panic about the troll, Dumbledore shoots several fireworks out of his wand. In Deathly Hallows, we learn that his wand is the Elder Wand.
  • The Snitch from Harry's first Quidditch match becomes important again towards the end of Deathly Hallows.
  • Ron's skill at wizard chess is established before Christmas and comes in handy later in the book.
  • Two of Harry's Christmas presents are important later. Hagrid's flute is useful for lulling Fluffy to sleep later in the book, while his father's invisibility cloak from Dumbledore is important throughout the series and its true nature as one of the Hallows is revealed in Deathly Hallows, as well as the reason why Dumbledore was interested in it.
  • The Mirror of Erised is later used to hide the Philosopher's Stone.
  • On the way to the mirror, Harry and Ron pass "the ghost of a tall witch." This is the Grey Lady, A.K.A. Helena Ravenclaw, who has a similar cameo in Half-Blood Prince before her backstory is revealed in Deathly Hallows.
  • Dumbledore tells Harry that he can become invisible without using a cloak. He does so with a Disillusionment Charm, which first appears in Order of the Phoenix.
  • When Harry asks Dumbledore what he sees in the Mirror of Erised, he says a pair of woolen socks. What he actually sees, his family alive and well, is not revealed until Deathly Hallows.
  • The Elixir of Life produced by the Philosopher's Stone makes the drinker immortal. This hints at Voldemort's fear of death, which is revealed in Half-Blood Prince.
  • The first years learn about treating werewolf bites in Defense Against the Dark Arts. Come Prisoner of Azkaban, the teacher of that class is a werewolf.
  • At one point, Harry has the horrible feeling that Snape could read minds." We learn in Order of the Phoenix that such an ability is known as Legilimency, though Snape is adamant that it is more complicated than simply reading minds.
  • For a Quidditch victory party, Fred and George steal cakes from the kitchens. Goblet of Fire reveals that they're actually quite friendly with the House-elves.
  • Harry looks up Dittany while studying. This plant reappears in Half-Blood Prince and Deathly Hallows for treating severe injuries.
  • Hagrid says he won a dragon egg off a stranger in the village. The stranger turns out to be Quirrel while the village, Hogsmeade, becomes an important location starting in Prisoner of Azkaban.
  • Filch says that he keeps chains in his office in case he's ever allowed to use them again. He almost gets the chance in Order of the Phoenix, though Umbridge is sacked before she can pass Educational Decree 29.
  • Malfoy claims there are werewolves in the Forbidden Forest. When the nature of werewolves is explained in Prisoner of Azkaban, his claim is revealed as anti-werewolf prejudice which is a part of the series from that book on.
  • The centaurs reappear in Order of the Phoenix are important to the plot.
  • Both Ronan and Bane say that "Mars is bright tonight." In Order of the Phoenix, Firenze calls Mars the "bringer of battle." Their divination predicts that war is coming, and it eventually does.
  • Quirrell drinks unicorn blood to make Voldemort stronger. Unicorn blood is later used in Goblet of Fire as one of the ingredients to give Voldemort a body. Firenze also says that drinking unicorn blood curses the drinker, which seems accurate given that the rest of Quirrell's life is unpleasant and short.
  • Hermione says McGonagall told her that fortune-telling is "a very imprecise branch of magic." This is greatly expanded on in Prisoner of Azkaban, with Professor Trelawney's Divination class.
  • Hagrid mentions having won the dragon egg at the Hog's Head, which appears in every book from Prisoner of Azkaban on.
  • The trio goes to find Dumbledore only to realize they have no idea where his office is. The headmaster's office first appears in the next book.
  • McGonagall says that Dumbledore flew to the Ministry of Magic. In Order of the Phoenix it is revealed that he rides one of the school's Thestrals when he doesn't feel like Apparating.
  • Harry says that if Voldemort takes over, he would turn Hogwarts into a school for the Dark Arts. This is exactly what he tries to do in Deathly Hallows and succeeds in doing in the bad timeline in Cursed Child.
  • The Devil's Snare is briefly important here and again in Order of the Phoenix.
  • Harry dreads encountering a fully-grown dragon on the way to the Philosopher's Stone. He doesn't, but in Goblet of Fire...
  • Harry realizes that he would be no match for Snape. When they duel at the end of Half-Blood Prince, this is proven true.
  • Quirrell reveals that Snape's hatred of Harry is due to his father James. The full scope of the situation is revealed over the course of the series and is not fully understood until Deathly Hallows.
  • Dumbledore says that "humans do have a knack of choosing precisely those things that are worst for them." Even he is not immune to this, as in Half-Blood Prince his desire to use the Resurrection Stone led him to impulsively try on Marvolo Gaunt's ring, causing him to be mortally cursed.
  • Dumbledore says that Voldemort is not truly alive, and thus cannot be killed. The details of this are revealed in Half-Blood Prince.
  • Harry asks Dumbledore why Voldemort tried to kill him in the first place, but Dumbledore declines to answer. The prophecy is revealed in Order of the Phoenix.
  • Dumbledore tells Harry that James saved Snape's life, the circumstances of which are revealed in Prisoner of Azkaban. He also claims that this is why Snape protected Harry from Quirrel, though Deathly Hallows reveals that he actually did it out of love for Lily.
  • Hagrid gives Harry a photo album with pictures of his parents from their old school friends, one of whom was undoubtedly Remus Lupin, who first appears in Prisoner of Azkaban.
  • It is mentioned that Neville got good marks on his herbology exam. His interest and talent for the subject grows throughout the series until, by the epilogue of Deathly Hallows, he becomes the Hogwarts herbology professor.
  • The trio expresses amazement that Gregory Goyle managed to pass his exams. In Deathly Hallows, he becomes quite adept at the Dark Arts.
  • The students are given notes forbidding them from using magic over the summer holiday, presumably mentioning the Decree for the Reasonable Restriction of Underage Sorcery, which is a plot point later that summer in Chamber of Secrets and again in Order of the Phoenix.
  • Ron promises to send Harry a letter inviting him to stay. He later does, only to have it stolen by Dobby before it can arrive prior to Chamber of Secrets.
  • In the last line of the book, Harry says he's "going to have a lot of fun with Dudley this summer..." Chamber of Secrets reveals that this is not the case, and that the Dursleys immediately lock up all of his magical possessions.

    Harry Potter and the Chamber of Secrets 
  • Dobby almost speaks ill of the family he serves. They are later revealed to be the Malfoys.
  • Dobby warns Harry of a plot to make bad things happen at Hogwarts. This refers to Lucius Malfoy, acting on orders given to him by Voldemort before his fall, to send his diary to Hogwarts to open the Chamber of Secrets and purge the school of Muggle-borns.
  • Harry receives a warning letter from Mafalda Hopkirk of the Improper Use of Magic office. She also sends him a notice in Order of the Phoenix and is impersonated by Hermione in Deathly Hallows.
  • Harry is threatened with expulsion should he perform any more magic, which is his fear in Prisoner of Azkaban and briefly happens in Order of the Phoenix.
  • The flying Ford Anglia is used to take Harry from the Dursley's house. Then again to fly to Hogwarts and then to escape from the Acromantulas in the Forbidden Forest.
  • Fred says that Muggle lock picking is worth learning. He and George later sell Muggle magic tricks at their joke shop in Half-Blood Prince.
  • The Weasleys have a ghoul in their attic. It serves an important function in Deathly Hallows, disguised as a Spattergroit-infected Ron.
  • George references Percy's strange behavior, which continues through the book. It is eventually revealed that he has a girlfriend, Penelope Clearwater.
  • Ron mentions Arthur's co-worker Perkins, who makes minor appearances in Order of the Phoenix and Deathly Hallows.
  • Harry hears Celestina Warbeck over the radio. One of her songs shows up in Half-Blood Prince.
  • Gilderoy Lockhart first appears in a photograph on a book cover, and is later a major character throughout the book.
  • Arthur mentions that Mundungus Fletcher tried to hex him during a raid. He is mentioned again in Goblet of Fire and then becomes an important character from Order of the Phoenix on.
  • Ron has a fish tank full of frog spawn in his room. When Harry returns in Goblet of Fire, he notes that this has grown into a large frog.
  • Ron still has his unexceptional pet rat Scabbers, who is revealed to be Peter Pettigrew in Prisoner of Azkaban.
  • When life at the Burrow is first described, we are told that "small explosions from Fred and George's bedroom were considered perfectly normal." In Goblet of Fire, it turns out that the explosions were a side effect of the twins working on joke products they hope to eventually sell.
  • The O.W.L.s are mentioned for the first time. They become important to the plot in Order of the Phoenix.
  • When Harry accidentally transports himself to Borgin and Burkes, he encounters a number of things that are important later in Half-Blood Prince. First, he hides inside a large black cabinet and is careful to leave the door open a crack. Had he shut it all the way, he would have learned a few years early that it is a Vanishing Cabinet with a twin located at Hogwarts. Draco examines a cursed opal necklace that "Has Claimed the Lives of Nineteen Muggle Owners to Date" and the Hand of Glory, both of which he will later use in his attempt to assassinate Dumbledore. The store itself makes an important reappearance in Half-Blood Prince, where we also learn that Voldemort used to work there to gain access to rare heirlooms for Horcruxes.
  • Lucius Malfoy arranges for Borgin to collect Dark Artifacts from Malfoy Manor, which is an important location in Deathly Hallows.
  • Fred, George, and Lee Jordan buy Filibuster Fireworks at Gambol and Japes. They shoot some off on the last day of vacation, George forgets the box when they are leaving to go to King's Cross, then he and Fred attempt to feed one to a Salamander at Halloween, and finally Harry uses one to create a diversion in Potions class so Hermione can obtain the last two ingredients they need for the Polyjuice Potion.
  • Ron tells Hermione and Harry that Percy wants to be Minister for Magic. Percy embarks on his Ministry career in Goblet of Fire and Hermione actually becomes the Minister for Magic by the time of Cursed Child.
  • The inconsiderate Daily Prophet photographer is identified as Bozo and accompanies Rita Skeeter in Goblet of Fire.
  • Draco calls Ginny Harry's girlfriend. They end up dating in Half-Blood Prince and get married before the epilogue of Deathly Hallows.
  • Lucius picks up Ginny's copy of A Beginner's Guide to Transfiguration and returns it to her cauldron. It is later revealed that he also slipped Tom Riddle's diary into her stack of books.
  • The spell Arthur used to enlarge the interior of the car is an Undetectable Extension Charm, which shows up later on, most notably with Hermione's handbag in Deathly Hallows and Newt Scamander's suitcase in the Fantastic Beasts film.
  • The Weasleys have to stop because Ginny forgot her diary, or, more accurately, Tom Riddle's diary, at home.
  • When Harry and Ron try to get to Platform 9 3/4, the barrier is blocked. They later learn this was done by Dobby.
  • Ron mentions Apparition by name, which later becomes an important method of transportation later in the series.
  • The Hogwarts Express Trolley Witch receives another mention. She does not get any expansion until Cursed Child.
  • Ron crashes the flying Ford Anglia into the Whomping Willow, which becomes far more significant in Prisoner of Azkaban.
  • Harry and Ron miss Ginny being sorted in Gryffindor. They also miss the sortings of Luna Lovegood (Ravenclaw) and Zacharias Smith (Hufflepuff) who first appear in Order of the Phoenix.
  • Ron speculates that Snape was sacked. In Deathly Hallows, Snape's tenure as Headmaster comes to an end when he is "sacked" by the Heads of House.
  • Harry notices Dumbledore's "very crooked" nose, which is explained in Deathly Hallows.
  • The second years repot Mandrakes in their first Herbology lesson. Hermione explains their curative effects, which is critically important later in the book to restore those petrified by the basilisk and the fatal cries of adult Mandrakes, which comes up again in Deathly Hallows when they're used as part of the defensives measures during the Battle of Hogwarts.
  • Justin Finch-Fletchley makes his first appearance in this lesson a while before he has an impact on the plot.
  • Ron's broken wand, with spells backfiring on him, is mostly used for comic relief throughout the book. However, it ultimately saves Ron' and Harry's memories when Lockhart attempts to obliviate them with it.
  • Ron's jealous rage over Hermione's crush on Lockhart is the first hint at his attraction to her that develops across the series.
  • Ron angrily tells Malfoy to "eat slugs." He later attempts to curse him with a spell that does just that, only to have it backfire.
  • Lockhart brings Cornish Pixies to class. Cornwall is where Shell Cottage is located in Deathly Hallows and it is the childhood home of Muggle private detective Cormoran Strike.
  • Draco Malfoy calls Hermione "filthy little Mudblood" and it is stressed upon how highly offensive the term is to Muggleborns. In Order of the Phoenix, we learn that, in the past, Snape called Harry's mother that, which was the catalyst for half the events in the series.
  • Hagrid tells the trio that the Defense Against the Dark Arts position is rumored to be jinxed. Sure enough, no teacher holding that post lasts for more than one school year throughout the series. In Half-Blood Prince, we learn that Voldemort himself cursed the job when he was denied it.
  • Ron alludes to the concept of pure-blood supremacy, which is important later in the book and is a central tenet of the Death Eaters' philosophy later in the series.
  • Hagrid's expulsion from Hogwarts is brought up again, and is explained later in the book.
  • Lockhart receives fan mail from Gladys Gudgeon, who continues to do so in Order of the Phoenix after he's been erased of his memories, exposed as a fraud, and permanently institutionalized in St. Mungo's.
  • During his detention with Lockhart, Harry hears a voice talking about killing. This is coming from the basilisk slithering around in the pipes.
  • Dumbledore inspects the petrified Mrs. Norris with his wand, which, as we learn in Deathly Hallows, is the Elder Wand.
  • Ron mentions vomiting slugs all over an Award for Special Services to the School during his detention with Filch. This trophy, as he later remembers, was awarded to Tom Riddle, A.K.A. Voldemort.
  • At the beginning of October, Ginny is mentioned to be looking pale. This is the first of many signs that something is not quite right with her.
  • Peeves smashes a Vanishing Cabinet, the twin of the one in Borgin and Burkes, which comes up again in Order of the Phoenix, and then is critical to the plot of Half-Blood Prince, when Malfoy spends all year mending it to use in his attempt to assassinate Dumbledore.
  • Fred and George steal a salamander from their Care of Magical Creatures class. Not only do the trio begin taking this class in Prisoner of Azkaban, the current professor Silvanus Kettleburn retires and is replaced by Hagrid.
  • Hermione says that Moaning Myrtle's bathroom has been closed all year because she keeps flooding it. Not only is Myrtle a victim of the basilisk, the bathroom was flooded by the basilisk itself. The bathroom itself is vastly important later in the book, as the trio uses it to brew Polyjuice Potion and it contains the entrance to the Chamber of Secrets.
  • The spiders acting strangely eventually leads Harry and Ron to Aragog and is a sign of the Basilisk.
  • Polyjuice Potion is used relatively innocently here, but later in the series it becomes an important tool for good and for evil.
  • Dobby tells Harry that if he can only be freed if his masters present him with clothes, and that if he was presented with even a sock, he would be free to leave his masters' house for ever. At the end, Harry tricks Lucius Malfoy into doing just that, releasing Dobby from servitude.
  • Dumbledore says the question is not who opened the Chamber of Secrets again, but how. He already knows that Tom Riddle opened it in the first place, he just doesn't have any evidence to prove it, and can't explain how he's managed it this time.
  • "Talismans, amulets, and other protective devices" become very popular at Hogwarts after the Chamber is opened. This happens again in the wider wizarding world in Half-Blood Prince after Voldemort's return.
  • Seamus says that dueling lessons "might come in handy one of these days..." Indeed they do, when the Second Wizarding War begins.
  • Harry learns his signature spell - Expelliarmus, the Disarming Charm - from Snape, of all people, at the Dueling Club.
  • After Ron and Hermione learn Harry is a Parselmouth, they worry that people will think he's Salazar Slytherin's "great-great-great-great-grandson." He's not, but the piece of Voldemort's soul living in him is indeed descended from Slytherin.
  • Hagrid speculates that his roosters were killed by foxes or a Blood-Sucking Bugbear. They were actually killed by Ginny.
  • Previous Hogwarts Headmasters appear sleeping in their portraits. These include Armando Dippet (who is important in the backstory of this book), Dilys Derwent and Dexter Fortescue (who are important in saving Arthur Weasley's life in Order of the Phoenix), and Phineas Nigellus Black (who becomes very important in Deathly Hallows).
  • Harry encounters the Sorting Hat again. It shows up later in the book during a critical moment.
  • When Harry meets Fawkes, Dumbledore explains that Phoenixes can carry enormous weight and their tears have healing powers, both of which are very useful later in the book. They also regularly die and then return to life, which allows Fawkes to intercept Voldemort's Killing Curse meant for Dumbledore in Order of the Phoenix. Fawkes himself is the Phoenix who gave the feathers for Voldemort' and Harry's wands, as revealed in Goblet of Fire.
  • While disguised as Crabbe and Goyle, Ron and Harry run into a Ravenclaw girl who later turns out to be Penelope Clearwater, who gets petrified by the basilisk. She was also in the general vicinity of Percy, who she is dating.
  • A Daily Prophet article mentions that Lucius Malfoy is one of the Hogwarts governors, which is important later in the book for getting Dumbledore suspended as Headmaster.
  • Malfoy says that the last time the Chamber was opened, a Muggle-born died. This turns out to be Moaning Myrtle.
  • Malfoy is the first to mention Azkaban, the wizard prison. Hagrid is sent here later in the book, and, obviously, it becomes important from Prisoner or Azkaban on.
  • Malfoy unknowingly reveals to Harry and Ron that Malfoy Manor has a "secret chamber under the drawing-room floor." This is used in Deathly Hallows to imprison Ollivander, Luna, Griphook, Dean Thomas, and, briefly, Harry and Ron.
  • The trio discovers the diary of T.M. Riddle in the bathroom. This turns out to be the thing responsible for Ginny opening the Chamber of Secrets, and, as we learn in Half-Blood Prince, one of Voldemort's Horcruxes. T.M. Riddle is revealed to be Voldemort himself.
  • Ron jokes that Riddle earned his Award for Special Services to the School by killing Myrtle. In fact, he actually is directly responsible for her death.
  • Lockhart mentions Love Potions on Valentine's Day, and they become very important in Half-Blood Prince when Ron drinks one and we learn Voldemort was conceived under its influence.
  • Ginny is noted to be horrified when Malfoy takes the diary from Harry. She later ransacks the second year boys' dormitory to retrieve it.
  • Riddle tells Harry that he stored his memories in the diary in a "more lasting way than ink." In Half-Blood Prince, the method is revealed to be storing a piece of his soul in it.
  • Harry travels into Riddle's memory. This type of magic becomes important from Goblet of Fire on with Dumbledore's Pensieve.
  • Riddle talks about his early years to Professor Dippet and, later in the book, to Harry. This is greatly expanded upon in Half-Blood Prince.
  • In Riddle's memory, Harry catches a glimpse of Aragog, who is important later in the book.
  • The second years sign up for third year electives. Harry and Ron take the same classes, which are revealed in Prisoner of Azkaban to be Divination and Care of Magical Creatures, while Hermione signs up for them all, and will receive a Time-Turner in able to accomplish this.
  • Percy advises Harry to play to his strengths, and Harry feels that his only strength is Quidditch. A similar exchange takes place with far more importance between Harry and Professor Moody in Goblet of Fire prior to the First Task.
  • Hermione rushes off to the library after Harry hears the voice again, and she gets petrified. We later learn that she tore out a page on Basilisks and was on her way back, checking around corners with a mirror when she and Penelope Clearwater were attacked.
  • When Percy finds out about Penelope Clearwater, he is left in shock, presumably because he didn't think the monster would dare attack a prefect. We later learn that she is actually Percy's girlfriend.
  • Harry's Invisibility Cloak makes another appearance. It becomes even more important in Deathly Hallows when we learn that it's one of the Deathly Hallows.
  • Hagrid accuses Lucius Malfoy of threatening and blackmailing the other Hogwarts governors. This turns out to be exactly the case.
  • Lucius mentions the "Azkaban guards," i.e. the Dementors, who make their first appearance in Prisoner of Azkaban.
  • Dumbledore says that he'll only truly be gone when no one left is loyal to him, and that help will always be given at Hogwarts to those who ask for it. This is important later in the book.
  • Lucius says that hopefully Dumbledore's successor will be able to prevent any killings. In Deathly Hallows, his legitimate successor Snape discreetly tries to protect students from the Carrows.
  • After Dumbledore's suspension, Malfoy suggests to Snape that he should apply for the position of Headmaster. In Deathly Hallows, this is where he winds up.
  • Ron is scared that there are werewolves in the Forbidden Forest. This is another instance of the ignorance and prejudice faced by werewolves that becomes apparent in Prisoner of Azkaban.
  • Harry mentions the centaurs, who become important in Order of the Phoenix.
  • Percy reveals that Ginny walked in on him doing something embarrassing, later revealed to be kissing his girlfriend Penelope.
  • Harry and Ron hide in the staffroom wardrobe. A boggart takes up residence there in Prisoner of Azkaban.
  • Myrtle mentions having haunted her former bully Olive Hornby after becoming a ghost. This is expanded upon in Goblet of Fire.
  • Riddle tells Harry about Ginny's crush on him, which is important from Half-Blood Prince on.
  • Riddle falsely claims Hagrid used to raise werewolf cubs under his bed. Voldemort tells the same bigoted joke in regards to the marriage of Lupin and Tonks in Deathly Hallows.
  • Riddle says Dumbledore never like him as much as the "other teachers," one of whom was Horace Slughorn, a major character in Half-Blood Prince.
  • Riddle mentions his "most intimate friends," who are revealed in Half-Blood Prince to have been the earliest Death Eaters and included Antonin Dolohov and Nott as well as the elder Lestrange, Rosier, Avery, and Mulciber.
  • We learn in Deathly Hallows that Gryffindor's sword was imbued with Basilisk venom, which enables them to use it to destroy other Horcruxes, specifically the ring, the locket, and the snake.
  • Ron and Hermione return to the Chamber of Secrets in Deathly Hallows to retrieve a Basilisk fang and destroy Hufflepuff's cup.
  • Dumbledore says that Voldemort underwent "dangerous, magical transformations" in the past, which we learn in Half-Blood Prince to be splitting his soul into pieces.
  • Dumbledore tells McGonagall to alert the kitchens for a feast. In Goblet of Fire, we learn that it is staffed by house-elves, and Dobby becomes employed there.
  • Dumbledore tells Harry that he suspects a part of Voldemort may live inside him. In Deathly Hallows, this proves true and Harry turns out to be an unintentional Horcrux.
  • Dumbledore points out that only a true Gryffindor could pull Godric Gryffindor's sword out of the Sorting Hat. In Deathly Hallows, Neville definitively proves that he belongs in Gryffindor when he summons the sword and kills Voldemort's final Horcrux (which is also a snake).
  • Dumbledore says that he needs to hire a new Defense Against the Dark Arts Professor. In Prisoner of Azkaban, he ends up hiring Remus Lupin.
  • Dobby reappears in Goblet of Fire, becoming an important character from then on.
  • The last we hear of Lockhart, he's being sent off to get his memories back. When he reappears at St. Mungo's in Order of the Phoenix, he's not much better off.
  • At the end, Harry gives Ron the Dursleys' telephone number. Ron ends up calling at the beginning of Prisoner of Azkaban, with disastrous results.

    Harry Potter and the Prisoner of Azkaban 
  • On the first page, Harry is reading A History of Magic by Bathilda Bagshot, who becomes important in Deathly Hallows.
  • The newspaper photo of the Weasley family's vacation to Egypt is used by Sirius Black to realize Peter Pettigrew is alive, and thus is the catalyst for the entire plot of the book.
  • The Firebolt. Harry sees it first in Diagon Alley, and later gets one for Christmas from Sirius after his Nimbus is smashed by the Whomping Willow. He uses it in book 4 for the first task in the Triwizard Tournament, and in book 5 to get from the Dursley's house to 12 Grimmauld Place.
  • The tunnels leading out of Hogwarts, and the Marauder's Map. Harry uses the tunnels to get to Hogsmeade twice, using the map, and the one under the Whomping Willow is used to get to the Shrieking Shack built to smuggle Lupin out of the castle at the full moon. After the map is confiscated by Lupin he learns from it that Pettigrew is alive (in the film, Harry tells Lupin that he saw Pettigrew on the map, arousing his suspicion in the first place). The map turns out to have been written by Lupin himself, along with Sirius, Pettigrew and James Potter, and after Lupin returns it at the end of the book, it goes on to help Harry and the others throughout the rest of the series.
  • Crystal balls. Mentioned first by Trelawney in her first Divination class, then it turns out to be part of the Divination exam later in the same book. Trelawney uses crystal balls as weapons in the battle of Hogwarts in book 7, where she uses one to take out Fenrir Greyback.
  • Chekhov's Gunman: Sirius was mentioned in passing way back in the first chapter of the first book. This is when the reader really starts to realize just how much planning went into these books, and kicked off the frenzied search for what other hints and clues might pay off later.
    • Also Scabbers, AKA Peter Pettigrew, and to a much lesser extent Crookshanks.
    • Professor Trelawney, at the end of the book, Dumbledore casually mentions that he should give her a raise, since the prediction she made about Wormtail turned out to be true, and that it was the second accurate prediction she had ever made. At the end of OotP, it's revealed what the first one was.
  • Snape seemed to be the only teacher zealously trying to find Sirius. He's even willing enough to kill him and eager enough to watch the dementors suck out his soul. We find out that Sirius was a bully in the fifth book, and that Snape, like most people, thought that Sirius had led Voldemort to James and Lily. The seventh book reveals Snape's feelings for Lily.
  • Also, quite a few of the predictions done in the Divination Classroom turn out to be truer than one would've thought!
    • Ron: So...you're gonna suffer...but you're gonna be happy about it...
    • Just a few sentences later we also know that Harry will work for the ministry (As an auror, no less), get unexpected fortunes (from winning the Triwizard tournament the next year) and die. Even if it happens a lot later (and under different circumstances) than expected.
    • Trelawney also predicts that Hermione drops out of Divination class by Easter. Even if she probably did not know it herself at the time.
    • Trelawny continues to predict a grim in Harry's life. A Grim resembles a large black dog according to this book...and boy howdy does a large black dog (Sirius Black's animagus form) play a part in Harry's life by the end of this book and through book 5.
    • Furthermore, she claims the grim is an omen of death. It is. Just not for Harry.
    • Trelawny also tells Parvati Patil to beware a red-haired man. Ron goes out with her sister the next book...
  • The spy who tipped Dumbledore off that Voldemort was going after the Potters was Snape.
  • The sneakoscope that Ron thought to be broken because it kept spinning when Scabbers was near it.

    Harry Potter and the Goblet of Fire 
  • Mad-Eye Moody gives Neville a book on magical water-plants at the beginning of the year. This is actually Barty Crouch Jr., and he gave it to Neville to invoke this trope, hoping that Harry would be willing to ask anyone for help figuring out how to breathe underwater and would learn about gillyweed from him. It didn't work.
  • Chekhov's Gunman: Bertha Jorkins, Bellatrix Lestrange, Barty Crouch, Jr, Gregorovitch.
    • A more specific example related to Bertha Jorkins, her having been traveling in Albania when she was caught, her Memory Charm broken, and she was forced to divulge the truth about Barty Crouch, Jr. Why? Albania is where Helena Ravenclaw hid her mother's diadem, and where Voldemort later found it so as to take it to the Room of Requirement. And it's highly likely this is where Quirrell was traveling when he encountered Voldemort's spirit and became corrupted/possessed; he was supposed to have been in the Black Forest, which shows he was already moving around Europe.
  • Chekhov's Gunsnake: Nagini is introduced in the seemingly unrelated first chapter and is not featured significantly until the next book, when Voldemort orders her to attack Arthur Weasley and Harry is able to see the scene not only through Voldemort's eyes, but through Nagini's, possibly because they're both Voldemort's Horcruxes.
  • Dumbledore's brief look of triumph when he is told that Voldemort used Harry's blood to resurrect himself. Dumbledore just realized that Voldemort had just made it possible for Harry to survive the Killing Curse again.
  • Chekhov's Skill: The Unforgivable Curses.
    • The flash of green light Harry kept remembering in the first book. Revealed in this book to be the killing curse.
    • Neville reacting badly to the Cruciatus Curse. Later in that book, we find out why...
    • Accio spell. Taught in Flitwick's class earlier in the book. Harry struggles with it and then finds out it's the only way to get his broom to him to survive the first task. He eventually gets it right and uses it successfully not only in the tournament but to call the Tri-Wizard cup to him in the graveyard allowing him to take Cedric's body and himself back to Hogwarts.
  • Trelawney says she has seen the death descending over Hoggwarts in the crystal ball and looks preoccupied at Harry while saying so. At the end of the year Cedric dies. In front of Harry.
  • Harry and Ron seem to be great seers themselves. When to made up prophecies for their Divination assignment, quite a few seem to be accurate:
    • Harry predicts he is in danger of burns; the first Triwizard task is to outsmart a dragon.
    • Ron predicts Harry would be disappointed by someone he thought was his friend, which could either mean Ron's behavior toward Harry after he was chosen as a Triwizard champion, or Mad-Eye Moody actually being a Death Eater in disguise. He also predicts drowning twice, which Hermione points out. The second Triwizard task takes place in the lake, with Ron and Hermione having to be rescued from the merpeople.
  • During the Yule Ball, Dumbledore makes mention of having a Potty Emergency and discovering a room with "a really rather magnificent collection of chamberpots. When I went back to investigate more closely, I discovered that the room had vanished". Perhaps, Dumbledore theorizes, the room only appears when somebody really, really needs it...
  • After Hagrid is embarrassed by Rita Skeeter, and wishes to resign because of the public disgrace, Dumbledore tells him that his brother Aberforth had been convicted for practicing inappropriate charms on a goat. This is the first mention of Aberforth, but he becomes vitally important in Book 7.
  • A throwaway line from Amos Diggory at the beginning, when he meets Harry, Hermione and the Weasleys to go to the Quidditch World Cup: "The Lovegoods have been there for a week already." We think these are just random people they know until meeting Luna in the next book and her father in Book 7.

    Harry Potter and the Order of the Phoenix 
  • The once-mentioned locket that nobody could open when Number 12 Grimmauld Place was being cleaned out, which became important in book seven.
  • Harry begins having dreams early on in the story about locked doors and winding passages.
  • A portrait at St Mungo's insists Ron must have spattergroit; Ron retorts he's just freckled. In Deathly Hallows, Ron fakes being near death with spattergroit to follow Harry on the quest for Horcruxes and buy time to avoid Death Eaters coming after his family for helping Harry.
  • The thestrals, and Harry being able to see them.
  • Hermione makes a list containing the names of all the people agreeing to be in the DA. It's mentioned it that signing it feels unusually binding. Hermione cursed the list so that anyone who revealed the DA to the Ministry would break out in a rash. Not just any rash, either. It (permanently, per Word of God) writes 'Sneak' across their face.
  • In Chamber of Secrets, a passing mention was made to Peeves breaking a cabinet, preventing Harry from getting into trouble. It's mentioned here again, when the Weasley twins push one of Umbridge's hench-students in, and he gets trapped there for months because it's magical. In the next book, it's revealed to be linked with another cabinet outside the school, and Draco fixes it to let the Death Eaters in.
  • "Snape's Worst Memory". It involves Snape being publicly humiliated by Siruis, James and Peter, and provides an interesting Alternative Character Interpretation to James Potter (Jerk Jock, specifically). It's pretty bad on the surface... but in Book 7, we learn why it was his worst memory: it was the day he lost Lily forever (due to his own behavior, not really anything James did).
  • Chekhov's Gift: Near the middle of the book, Sirius gives Harry a magic mirror which is part of a pair that can enable the two holders to communicate magically. Sirius has the other one. Made horrifying when you realize that the driving point of the climax of the book is that Harry is trying to communicate with Sirius, but can't find a means to; only after Sirius has been murdered does he find the mirror in his school trunk. It's thrown away and broken, but a fragment of it becomes important in Deathly Hallows.
  • Chekhov's Gunman: Mrs Figg, introduced in Book 1 as Harry's baby-sitter, and then not mentioned again until briefly in Goblet and this book, which reveals her to be a squib and is the witness at Harry's trial who gets him acquitted.
    • The barman of the Hog's Head Tavern, identified two books later as Albus Dumbledore's younger brother Aberforth, who had been mentioned in passing by Dumbledore earlier. It was even noted that he "looked vaguely familiar"; this was because Harry had already seen him before, in the photograph of the original Order Of The Phoenix that Moody showed Harry during dinner at Number Twelve, Grimmauld Place.
    • Regulus Black, Sirius's brother who is mentioned in passing and the becomes important to the plot in Book 7.
    • Kreacher, a seemingly minor character who, in true JK Rowling style, ends up being important to both this book's plot and that of Deathly Hallows. When screenwriter Michael Goldenberg suggested writing him out of the movie adaptation, Rowling admitted, "If you do that, adapting Seven's going to be really difficult..."
    • Professor Trelawney. In Book 3 Dumbledore casually mentions that he should give her a raise, since the prediction she made about Wormtail turned out to be true, and that it was the second accurate prediction she had ever made. At the end, it's revealed what the first one was.
    • This is also the book where we start to see Neville's emerging combat skill, along with his determination, both of which become of great importance in Deathly Hallows.
    • This book also contains an example of what happens when you overuse Chekhov's Gunmen. Harry refers in passing to a Mark Evans while speaking to Dudley. This is a throw-away character who is never mentioned again, but many assumed he would have some importance in the future because he shares a same last name with Lily Potter (née Evans) and Petunia Dursley (née Evans). JK Rowling publicly apologized for it.
  • Chekhov's Skill: Occlumency. Harry never masters it, but Snape's talent in it is vital to his role as a spy.
  • The Quibbler, and the fact that Luna Lovegood's father is the editor. We meet him in Book 7.

    Harry Potter and the Half-Blood Prince 
  • When Harry hides his potions book in the Room of Requirement he marked the spot with a bust of a warlock wearing a wig and an old, battered tiara. Said tiara becomes immensely important in Book 7 when it's revealed to be the Lost Diadem of Ravenclaw, one of Voldemort's Horcruxes.
    • To add to that, the Room of Requirement itself. Draco was using it, specifically the Room of Hidden Things, to try and find a way to kill Dumbledore. The room is revealed in Book 7 to be the location of one of the Horcruxes, and Draco comes close to foiling Harry there because of how much experience he has with that room - as he says, "I virtually lived in the Room of Hidden Things last year." He knows how to get in.
  • Peruvian Instant Darkness Powder. Fred and George show it to Harry when he and the other Weasleys visit their joke shop in Diagon Alley, and mention how it could come in handy if one needs to make a quick escape. Come the end of the book where the school is infiltrated by Death Eaters thanks to Malfoy, and it does exactly that.
  • Chekhov's Boomerang: Felix Felicis. Harry acquires it from Slughorn during one of the Potions classes. Hermione thinks Harry spiked Ron with it for one of the Quidditch matches - he hadn't, he just wished them to think he had - and then Harry uses it to get the true memory from Slughorn where Tom Riddle asked him about Horcruxes.
    • Harry gives the Order of the Phoenix the rest of the potion when he and Dumbledore leave Hoggwarts, thinking that is when Malfoy is going to make his move. It gives Imperial Stormtrooper Marksmanship Academy to the attacking Death Eaters.
  • Tonks' Patronus changing its form. The fact that it's supposed to represent Lupin shows that the Patronus often represents someone the caster loves... much like Snape's.
  • During this years' only Hogsmeade trip, the trio encounter Mundugus again, selling things he stole from Grimmauld Place. The Hog's Head barman (Aberforth) was talking to him as they approached, and most likely acquired Sirius' mirror at that time, which becomes quite significant in the next book.
  • Romilda's love potions. Ron takes them on his birthday, and he falls in love with her, so naturally, Harry takes Ron to Professor Slughorn for a cure, but Prof. Slughorn ends up giving him poison....

    Harry Potter and the Deathly Hallows 
  • Harry's snitch, Dumbledore's Deluminator (aka the Put-Outer), Godric Gryffndor's sword, dragons at Gringotts, the poem warning thieves at Gringott's entrance, the eye Harry sees in Sirius's mirror, the tiara Harry put on a bust to mark a spot in the Room of Requirement, the locket in the House of Black, Wormtail's hand, Voldemort's claim about Wormtail's loyalty, Wormtail's debt to Harry, Harry's invisibility cloak, and the Basilisk's fangs.
    • Not to mention the protection charm cast by Lily which protect Harry from Voldemort. Harry's Heroic Sacrifice fuels the same charm, protecting all the students and staff of Hogwarts.
  • Chekhov's Boomerang: Sirius's mirror.
  • Chekhov's Gunman: Kreacher, Dobby, Aberforth, Grindelwald, Gregorovitch.
  • Chekhov's Gag: Movie-only. In the movies, Seamus had a Running Gag where he'd blow things up accidentally (usually in the background). Come the Battle of Hogwarts and McGonagall knows exactly who to turn to for the demolition of the Hogwarts bridge.
    • Trelawney's continued obsession with Harry's death finally comes to fruition in this book, though it's the one year where they don't interact until the very end and it doesn't take anyway.

http://tvtropes.org/pmwiki/pmwiki.php/ChekhovsGun/HarryPotter