Foreshadowing / Harry Potter and the Prisoner of Azkaban

• When Ron takes Scabbers to the Magical Menagerie, the witch at the counter remarks that ordinary common or garden rats shouldn't be able to live longer than about three years, whereas Scabbers has been in the family for much longer. Naturally, it turns out that Scabbers isn't a rat at all.
• Mr. and Mrs. Weasley discuss the threat to Harry one night in the Leaky Cauldron, and Arthur recounts why he believes Harry should be warned: Sirius Black successfully escaped from Azkaban and could therefore infiltrate Hogwarts, is reportedly obsessed with getting to Harry there ("He's at Hogwarts..."), and probably believes he'll be elevated to Voldemort's right-hand-man if he can best Harry, thus restoring his master to power. Only the first supposition is correct about Sirius, but all of them are correct about Barty Crouch Jr., primary antagonist of Book 4.
  • On that note, Sirius kept repeating "He's at Hogwarts" while in his cell. He never specified that he was referring to Harry Potter or anybody else.
• Harry uses Neville's name as his alias while on the Knight Bus. A few years later, Harry finds out that Neville was almost the chosen one instead of him.
• The apparently terrifying guards of Azkaban are brought up a few times in Chapter 3 and 4, making it clear that no one wants to interact with them more than they absolutely have to without actually naming who or what the guards are—for all the new reader knows, they're just ordinary witches and wizards with a sadistic streak and free rein to do whatever they want in their pursuit of Sirius Black. Come Chapter 5, we see why they're so feared: they're soul-sucking wraith-like monsters that practically personify existential dread.
• Lupin teaching Harry's class how to deal with the Boggart, a magical creature that is warded off with the combination of a spell and positive thoughts, foreshadowing him teaching Harry how to deal with Dementors. In this class, we learn that the Boggart can take on the form of a person's greatest fear. When Lupin steps in front of Harry to protect him from the Boggart-as-Dementor, the boggart turns into some sort of white orb that Ron identifies as a crystal ball. Or, as the movie shows much more explicitly, a full moon; what Lupin fears most of all is his werewolf transformation.
  • On that note, Snape spends the entire book Hint Dropping about Lupin's condition, in hopes that one of the students will catch on and get him fired. In the end, Snape himself spills the beans, which gets Lupin fired.
  • On the same note, Ron mentions that Lupin could have got Harry the Firebolt because he was apparently away when Harry's Nimbus 2000 was smashed by the Whomping Willow. Harry points out that Lupin was ill then, but Ron says that Lupin wasn't in the hospital wing, because he himself was there doing Snape's detention, and Harry would know too as he was in the hospital after falling off his broom. Lupin was sealed up in his office in werewolf form.
  • If you're into languages or into Roman mythology, Remus Lupin's very name will clue you in almost immediately to his true nature. Similarly, if you're into constellations, the name 'Sirius Black' will immediately tell you the identity of "the Grim".
• Dumbledore mentioning to Harry that Trelawney's latest prophecy brings her number of accurate prophecies up to “two”. The first one is the reason why Voldemort wants him dead.
• The conversation Hagrid mentions he had with Sirius Black foreshadows that he's not as bad as he appears to be.
• Ron wakes up in the middle of the night to find his curtains shredded and Sirius Black standing over him with a knife before fleeing when Ron screams. Everyone assumes Sirius is after Harry and went to the wrong bed, though Harry and Ron find it weird he didn't just kill Ron before moving on to Harry since he had no problem murdering bystanders thirteen years ago. Turns out Sirius did go to the right bed because Ron was letting Peter Pettigrew sleep there and Peter was the one Sirius was there to kill, as Peter betrayed Harry's parents to Voldemort and framed Sirius for it, along with killing all those muggles.
• An amusing note after Sirius Black breaks into Hogwarts the first time has the rumor mill going crazy, with Hannah Abott mentioning convincing others that Sirius Black could turn himself into an unasuming potted plant. While she's wrong about what he turns into, she is correct in her idea that Sirius is capable of physical transformation.
• Harry and Ron taking note of Hermione seemingly disappearing from right behind them after the Potions class at the start of chapter seven, only to reappear seconds later further behind them. When asked how she did it, Hermione replies "I had to go back for something." She had used the Time-Turner we find out about near the end.
• During the Divination exam, Harry makes up a story about seeing a Hippogriff flying away in a crystal ball. This foreshadows Buckbeak's eventual escape courtesy of Harry and Hermione using the Time-Turner.
• Neville tells Ron and Harry that Trelawney said he'll have a horrible accident if he talks to anyone about the test. Right before Harry goes, Ron tells Harry how he did. That night, Ron breaks his leg.
• Harry's two Quidditch-related dreams foreshadow two following books:
  • After the match against Ravenclaw, Harry dreams about following a silver shape through a forest, together with a galloping shape before coming to a clearing, foreshadows both Harry's own Patronus (a stag) and the scene in Book 7 where Harry follows Snape's Patronus (a doe) through a forest into a clearing.
  • Before the Quidditch final, Harry dreams that the Slytherins came to the match riding dragons and that he has to dodge the dragons' fire on his broom. Cue Book 4, where Harry dodges a dragon on his broom in the first Triwizard task.
• Professor Trelawney mentions Voldemort's servant returning him to life.
• This book introduces us to Sirius Black, named after the constellation Sirius. Notice how the only other similarly-named character in the books is Draco Malfoy? That's not an accident. As we learn in Book 5, Draco's mother Narcissa is Sirius' first cousin, and the twisted history of the Noble and Most Ancient House of Black becomes a major source of drama in the later books.
• The Dementors' storming the Quidditch match and attempting to give Harry the Dementor's Kiss are the first hints that the Ministry's control over them is limited.
• The Christmas dinner scene. Dumbledore offers Trelawney a chair, but she is panicked because if she sits the first to rise will die because there will be thirteen people at the table. But there already were thirteen people, because Scabbers, AKA Pettigrew, was in Ron's pocket. In Book 6, Dumbledore dies, the first of the attendees to rise.
• Dumbledore mentions that sparing Wormtail's life means Voldemort now has a servant who owes his life to Harry, and that there may be a time when Harry is glad that he did. In Book 7, when Harry is being strangled by Wormtail, Harry reminds him of this, which causes Wormtail to hesitate long enough for Harry to break free. Wormtail then gets strangled to death by his own magic hand (the result of a curse put on it by Voldemort should Wormtail ever betray him).
• 'Give me a reason, only one reason, and I swear I will.' said by Snape to Sirius. Naturally at first, it seemed that Snape was lashing at Sirius for all the bullying he got at their hands. It is revealed in Book 7 that Snape loved Lily, and he blames Sirius for their deaths. Sirius was supposed to be the Secret Keeper, but they changed it to Peter Pettigrew at the last minute...
• When Harry and Hermione follow Ron down the tunnel into the Shrieking Shack, Harry looks at a destroyed armchair and says "Ghosts didn't do that". This is an early clue that the Shrieking Shack is not actually haunted, as Lupin explains later.
• In the first chapter, Ron tells Harry about Bill's Sneakoscope, a device designed to detect untrustworthy people in the vicinity. When the Sneakoscope goes off at the Weasley family dinner, Bill assumes it's a malfunction, and Ron thinks it detected one of Fred and George's pranks. It's actually because of Peter Pettigrew/Scabbers.
• In the movie, Mr. Weasley asks Harry not to go looking for Sirius. Harry asks "Why would I go looking for someone who wants to kill me?" The scene then cuts to Peter Pettigrew/Scabbers.
• Peeves name-drops Sirius as the one who attacked the Fat Lady's painting while trying to get into the Gryffindor Common Room at the end of Chapter 8. The artwork for the very next chapter (appropriately titled "Grim Defeat") depicts the Grim aka Sirius' Animagus form.

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