Foreshadowing / Harry Potter and the Chamber of Secrets

• "Potter, you've got yourself a girlfriend!" Not for another four in-universe and seven real world years, though. More seriously, when Ginny decides to confess, who does she go to? One of her older brothers? One of the teachers? No. She goes to Harry.
  • Related to that is how the day Ginny gets taken into the Chamber is described as "the worst day of Harry's life".
• Malfoy calling Hermione a Mudblood. This is the first time the concepts of pure-blood and Muggle-born are brought up in the series. This becomes important for the events of this book, as Muggle-borns are targeted by Tom Riddle and the Basilisk. In the later books, it is revealed that pure-blood supremacist ideas run rampant through wizarding society as Muggle-borns tend to suffer discrimination. In fact, the Death Eaters aim for a wizarding society free of Muggle-borns. In short: this small insult foreshadows later issues coming up in the later books.
• In Chapter Fourteen, when second-years sign up for electives to take next year, it mentions Hermione signed up for every class offered. This becomes a key plot point in Book 3.
• Lucius to Hagrid: "I would advise you not to shout at the Azkaban guards like that. They won't like it at all."
• "Sir, why don't you apply for the Headmaster's job?" Draco Malfoy to Snape. In Book 7, he becomes Headmaster.
• The fact that the first half of the book is spent with the Trio trying to figure out whether or not Malfoy's up to something. Four years later, it's Harry by himself, because nobody believes him. He was right this time.
• Ron jokes about Tom Riddle murdering Moaning Myrtle to earn his Special Award for Services to the School. Riddle did murder her; he got the award for sucessfully framing another student for her death.
• The first time Harry sees Tom Riddle's name, he has the strange feeling he knows Tom. He should—he'd had a chunk of his soul stuck to him since he was a year old.
• About three pages before we learn Riddle's identity, he's described as having a "high, cold laugh" that sounds eerie coming out of a sixteen-year-old. Harry, of course, has heard that exact same laugh before...
• On Valentine's Day, Lockhart suggests that students ask Snape to teach them how to make a love potion, whereupon the narration remarks that Snape had an expression that clearly said that anyone who turned up asking for a Love Potion would be force-fed poison. In Book 6, Ron inadvertently consumes both a potent Love Potion and a lethal poison in rapid succession, though admittedly neither came from Snape and the poison wasn't force-fed into him.
• Dumbledore says that Harry's ability to speak Parseltongue and similar matters are because of Voldemort inadverdently giving Harry some of his powers. "You mean, it put a piece of himself inside of me?" Yes, he did. It isn't until Book 7 that it's explained in a less blunt version.
• Harry casts a spell called Rictusempra at Malfoy which makes him double over in uncontrollable laughter. Four years later, he casts a similar-sounding spell against Malfoy which does more damage.
• When Harry stays with the Weasleys, the narration briefly mentions regular occurrences of explosions from the twins' room. Book 4 reveals that these sounds were them creating products for Weasleys' Wizard Wheezes.
• We're given a really strong indication of Snape's true loyalties in his reaction when he learns that Ginny's been kidnapped by the Heir. He may be a dick, but innocent people being in danger clearly horrifies him.
• After Lockhart’s first class:
  "Rubbish " said Hermione "you’ve read his books - look at all the amazing things he’s done-"
  "He SAYS he’s done" Ron muttered.
• The Vanishing Cabinet that Peeves drops and breaks. It reappears in its broken state for a minor moment in Book 5, where it's mentioned as a background event. The broken cabinet, and its repair, plays the main role in getting Death Eaters into Hogwarts in Book 6.
• In Borgin and Burkes, Harry inspects a necklace worth the sign "Do not touch! Cursed". In Book 6, Katie Bell gets cursed by this very necklace, after accidentally touching it during an argument with her friend.
• Also in Borgin and Burkes, Draco Malfoy is shown to be very interested in a dark artefact called the Hand of Glory, asking if he could buy it. At some point by book 6, he does this, and uses it during the Death Eater infiltration of Hogwarts.
• When Harry shows Riddle's diary to Dumbledore and McGonagall, Dumbledore is noted to be keenly looking at it. It's not because Dumbledore is amazed by what Riddle created. It's because Dumbledore recognizes it as a Horcrux and finally realizes what Voldemort did to make himself immortal.
• Every time an attack occurs, the narration makes sure to mention Ginny.
  • After Mrs. Norris is attacked:
    "Ginny Weasley seemed very disturbed about Mrs. Norris's fate. According to Ron, she was a great cat lover."
  • After Colin Creevey is attacked:
    "Ginny Weasley, who sat next to Colin Creevey in Charms, was distraught."
  • After the double attack on Justin and Nearly Headless Nick, Fred and George walk Harry to class, making jokes about him being the suspect.
    "Ginny didn't find it amusing either."
  • When Ginny sees Harry has the diary:
    "Ginny was staring from the diary to Harry, looking terrified."
  • When the trio visit Hagrid after the Quidditch practice, Hagrid offhandedly mentions he's seen Ginny roaming around the grounds, and he presumed she had been looking for Harry. We later find out she was looking for roosters to kill.
  • Not to mention in chapter 5 the third time the Weasleys have to turn back is because Ginny nearly leaves the diary behind.
• When they find the diary, Ron warns Harry that it could be dangerous. He's right.
• Cornelius Fudge's Establishing Character Moment is him throwing Hagrid into Azkaban because the latter was accused of opening the titular Chamber the first time. This comes across as Fudge prioritizing the Ministry looking good over ordering an investigation to try to get to the root of the problem. Fudge is revealed to be a full-fledged Bitch in Sheep's Clothing by the end of Goblet of Fire.

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