Note: There will be spoilers for those who have not finished the books.

8) Sirius Black

“Hagrid,” said Dumbledore, sounding relieved. “At last. And where did you get that motorcycle?”
“Borrowed it, Professor Dumbledore, sir,” said the giant, climbing carefully off the motorcycle as he spoke. “Young Sirius Black lent it to me. I’ve got him, sir.”

Most people probably read this at the very beginning of "Sorcerer's/Philosopher's Stone" and thought nothing of it. Sirius Black was just a name we registered and skipped over, until "Prisoner of Azkaban." We then realized that Sirius Black was actually Harry’s godfather, wrongly convicted of a crime he didn’t commit, who most likely gave Hagrid his motorcycle to make sure Harry got to safety and away from where his parents were just killed. The fact that J.K. Rowling introduced a character way before we ever actually meet him is a huge foreshadowing of things to come. If only we had known…

9) The Room of Requirement

“Oh I would never dream of assuming I know all Hogwarts’ secrets, Igor,” said Dumbledore amicably. “Only this morning, for instance, I took a wrong turning on the way to the bathroom and found myself in a beautifully proportioned room I have never seen before, containing a really rather magnificent collection of chamber pots. When I went back to investigate more closely, I discovered that the room had vanished. But I must keep an eye out for it. Possibly it is only accessible at five-thirty in the morning. Or it may only appear at the quarter moon - or when the seeker has an exceptionally full bladder.”
Harry snorted into his plate of goulash. Percy frowned, but Harry could have sworn Dumbledore had given him a very small wink.

In "Goblet of Fire," Dumbledore himself found the Room of Requirement, which Harry and his friends would later use in "Order of the Phoenix" to hide from Professor Umbridge. Although Dumbledore is known to be eccentric, he actually makes perfect sense here; although we don’t realize it until later on. At the time, we assume it’s just silly stories for the entertainment of those at the Yule Ball. The question remains, does Dumbledore then known through all of "Order of the Phoenix" where Dumbledore’s Army is practicing?

10) The Vanishing Cabinet

Harry looked quickly around and spotted a large black cabinet to his left; he shot inside it and pulled the doors closed, leaving a small crack to peer through. Seconds later, a bell clanged, and Malfoy stepped into the shop.

In "The Chamber of Secrets," Harry goes into a large cabinet to hide. Nothing strange about that right? But then…

“Malfoy just docked us all about fifty points,” said Harry furiously, as they watched several more stones fly upwards from the Gryffindor hour-glass.
“Yeah, Montague tried to do us during break,” said George.
“What do you mean, ‘tried’?” said Ron quickly.
“He never managed to get all the words out,” said Fred, “due to the fact that we forced him headfirst into that Vanishing Cabinet on the first floor.”
Hermione looked very shocked.
“But you’ll get into terrible trouble!”
“Not until Montague reappears, and that could take weeks, I dunno where we sent him,” said Fred coolly. “Anyway… we’ve decided we don’t care about getting into trouble any more.”

In "Order of the Phoenix," Fred and George are up to their usual pranks and trap Slytherin classmate Graham Montague in a broken vanishing cabinet in Hogwarts. We eventually learn that the cabinet makes Montague disappear in a weird space where he can hear things happening in both Hogwarts and Borgin and Burkes, where he literally goes crazy.

This cabinet is then moved to The Room of Requirement, which Draco Malfoy uses later in "The Half-Blood Prince" to smuggle Death Eaters into Hogwarts. The fact that had Harry stayed in that cabinet any longer, he could have been transported directly to school is a huge clue. What would have happened if he had discovered the true purpose of the cabinet sooner?

11) Aberforth Dumbledore

In "Goblet of Fire," Headmaster Dumbledore mentions his brother.

“Hagrid, look what I’ve got for relatives!” Harry said furiously. “Look at the Dursleys!”
“An excellent point,” said Professor Dumbledore. “My own brother, Aberforth, was prosecuted for practicing inappropriate charms on a goat. It was all over the papers, but did Aberforth hide? No, he did not! He held his head high and went about his business as usual! Of course, I’m not entirely sure he can read, so that may not have been bravery…”
“Come back and teach, Hagrid,” said Hermione quietly, “please come back, we really miss you.”

Then in "Order of the Phoenix," Harry and his friends are trying to start up a training group to combat Umbridge’s bad teaching. The chose to meet at the Hog’s Head bar, which is described as smelling like goats.

The barman sidled towards them out of a back room. He was a grumpy-looking old man with a great deal of long grey hair and beard. He was tall and thin and looked vaguely familiar to Harry.
“What?” he grunted.
“Three Butterbeers, please,” said Hermione.

But of course, Harry doesn’t make the connection until "Deathly Hallows" when he, Ron and Hermione need Aberforth’s help to get back into Hogwarts. We just assume there is a weird goat man running the bar and Dumbledore’s brother moved away after being persecuted.

12) Going Into Death

In "Prisoner of Azkaban," Arthur Weasley talks to Harry about Sirius Black, but it’s not Mr. Weasley’s words that foreshadow future events, it's Harry’s own response.

“Promise me, Harry,” said Mr. Weasley, talking more quickly still, “that whatever happens —”
“Why would I go looking for someone I know wants to kill me?” said Harry blankly.

But, in the "Deathly Hallows," that’s exactly what Harry does. He walks to his own death purposefully looking for someone who wants to kill him.

He pressed the golden metal to his lips and whispered, “I am about to die.”
The metal shell broke open. He lowered his shaking hand, raised Draco’s wand beneath the Cloak, and murmured, “Lumos.”
The black stone with its jagged crack running down the center sat in the two halves of the Snitch. The Resurrection Stone had cracked down the vertical line representing the Elder Wand. The triangle and circle representing the Cloak and the stone were still discernible.

And again, Harry understood without having to think. It did not matter about bringing them back, for he was about to join them. He was not really fetching them: They were fetching him.

BONUS: Scabbers the Rat/ Peter Pettigrew

In "Sorcerer's/Philosopher's Stone,"on the Hogwarts Express, Ron attempts a spell on his rat, Scabbers. The spell doesn't work.

“Oh, are you doing magic? Let’s see it, then.”
She sat down. Ron looked taken aback.
“Er — all right.”
He cleared his throat.
“Sunshine, daisies, butter mellow, Turn this stupid, fat rat yellow.”
He waved his wand, but nothing happened. Scabbers stayed gray and fast asleep.

Later in "Prisoner of Azkaban," we learn that Scabbers the Rat is really Peter Pettigrew in animagus form.

“No, Ron,” said Lupin. “Two of you.”
He had stopped his pacing, his eyes moving over Ron.
“Do you think I could have a look at the rat?” he said evenly.
“What?” said Ron. “What’s Scabbers got to do with it?”
“Everything,” said Lupin. “Could I see him, please?”
Ron hesitated, then put a hand inside his robes. Scabbers emerged, thrashing desperately; Ron had to seize his long bald tail to stop him escaping. Crookshanks stood up on Black’s leg and made a soft hissing noise.
Lupin moved closer to Ron. He seemed to be holding his breath as he gazed intently at Scabbers.
“What?” Ron said again, holding Scabbers close to him, looking scared. “What’s my rat got to do with anything?”
“That’s not a rat,” croaked Sirius Black suddenly.
“What d’you mean — of course he’s a rat —”
“No, he’s not,” said Lupin quietly. “He’s a wizard.”
“An Animagus,” said Black, “by the name of Peter Pettigrew.”

If the rat Ron had performed the spell on in the first year was actually a rat and not the animagus, would the spell have worked?

This is just barely scratching the surface of all the cool and crazy tidbits of information scattered throughout the wizarding world that J.K. Rowling created for us to enjoy.

Do you know a foreshadowing event or similar piece of cool information that isn't on my list? I'd love to hear about it!