For starters, let me say the books will always be better than the films. But the movies are great too and have earned their place in cinematic history. Also, there are times where the films are almost as deep and layered as the books, even including some foreshadowing and Easter eggs all throughout the series. So here are ten of them that I have noticed while watching the films:
1) Philosopher's Stone - Wizard in the Leaky Cauldron
In the Leaky Cauldron, a Wizard is shown reading Stephen Hawking's "A brief history of time" while steering his mug magically with no wand! While most Wizards and Witches distance themselves from Muggle sciences as it serves them no use, this guy is different and there is probably a more compelling story behind this than about The Boy Who Lived!
2) The Chamber of Secrets - Draco might have been a good guy all along
Like in the books, Draco is portrayed as an entitled bully who looks down on others. Of course, towards the end of the series, we learn he is not all that bad. But upon a closer look, we can see that the second film might have actually hinted that there might be some good in Draco, something its source material did not do. When the Basilisk was petrifying Muggleborns at Hogwarts, Harry and Ron only figured out what it was through a torn page from a book in a petrified Hermione's hand. Like the audiences, Harry and Ron assumed that Hermione wrote that as a clue. But why would book lover Hermione tear a page out of a book while she could have just borrowed? When Harry and Ron tell her that there is no way they could have cracked the case without her help, a cured Hermione looked somewhat confused. So, what if was Draco who did that to help kill the Basilisk? When Harry, Hermione, and the Weasleys are at Flourish and Blotts buying textbooks, they run into the Malfoys. Draco, knowing that nobody is looking, tears out a page from a seemingly random book. Why would a the rich Draco risk doing something like that? Perhaps he knows about his father, Lucious' plan for Muggleborns that year. Being the not-so-evil person he is, Draco somehow manages to slip the ripped piece of paper on basilisks into Hermione's hand at the hospital wing.
3) The Prisoner of Azkaban - Lupin's Skeleton Shaped Candles
Why in the world did Lupin need them since his office was already well lit? After each Bogart lesson, he reignites them, as if they must be lit all the time. The top vertebra of each candle is marked with 'VIII' and the numbers continue down the candle, which has 21 vertebrae. Could it be possible that they have to be constantly burning to measure time? Lupin could be marking the passage of time through the cycle of the moon. After each full moon, Lupin would light a new candle which burns through all 21 days of the cycle. On the 22nd day, he would start to take the Wolfsbane potion to prepare him for when the full moon begins.
4) The Goblet of Fire - The Dark Mark's hidden meaning
Looking closely at the Dark Mark, you will notice they way the snake swirls out of the skull actually forms the number eight. If you have read the books or at least watched the movies, you will know Voldemort accidentally made Harry his eighth Horcrux when trying to kill him as a baby. This is only done in the movies. In the books, however, it was merely described as "a colossal skull, comprised of what looked like emerald stars, with a serpent protruding from its mouth like a tongue". Could it be JK Rowling told the filmmakers to depict the serpent in the shape of a figure 8 to hint at the secret of Voldemort's immortality?
5) The Goblet of Fire - Pure blood supremacy
Voldemort's ideology shares many similarities with those that advocate white supremacy in the real world. Like Hitler, Voldemort kills masses to allow who he deemed the most superior race to rule the world. Like how Hitler was only part Aryan, Voldemort is also a half-blood. When Voldemort was defeated the first time, most of his surviving followers claimed they were under the Imperius Curse to escape the law. Similarly, many Nazis said they were forced to follow Hitler's orders for fear of their own lives. Both the Swastika and the Dark Mark represent a symbol of evil. Also, notice how the Death Eater's uniform are very similar to those worn by the Ku Klux Klan?
6) The Goblet of Fire - Foreshadowing an unreleased book
When Harry is talking to Dumbledore in his office after seeing the flashback of Barty Crouch Jr., he looks into one of his glass cabinets. In it, we can see the some kind of transparent, pyramid shaped object with a bronze sphere with a rod pierced through it. This objects resembles the Deathly Hallows symbol. Mind you, this film was released two years before the final book came out.
7) The Order of The Phonix - Voldemort in a Muggle suit
The scene where Harry sees Voldemort at the train station in a regular suit did not go down well with fans who claimed it was out of character for a Muggle-hating Dark Wizard to be appearing in such a way. Both the director and producer defended their decision to include this scene. This was a way to show Voldemort is taking control of Harry's mind and is able to taunt him. This foreshadows what happens towards the end of the film where Voldemort easily inflitrates Harry's mind and tricks him into coming to the Department of Mysteries.
8) The Half Blood Prince - Riddle's Hocruxes
Many fans, including me, were not happy that the filmmakers cut down on many scenes from Dumbledore's Pensive. The filmmakers claim they were trying to focus on Voldemort's rise rather than his background. Nevertheless, they did justice with the scenes which they did include. For example, when we see Dumbledore visiting the young Tom Riddle at the Muggle orphanage, there is a photograph on the wall of the same seaside cave that Dumbledore and Harry visit to search for the locket Horcrux. In the book, this place is described as the site where Riddle unknowingly used magic to torment other children from the orphanage while on a trip, meaning this place is probably where he first realized he was different and thus, has some significance to him. Also, notice how there are also seven rocks on his windowsill, which is the same number of Horcruxes he intended to create.
9) The Deadly Hallows Part 1 - Hermione's character development
At the start of the film, Hermione hears her parents talking about Australia while someone on TV is talking about a countryside. Hermione then quietly uses the Memory Charm to permanently erase memories of herself from her parents' minds. This is different from the book, where, Hermione mentions that she merely alters her parents memories with a False Memory Charm to give them new identities, a childless couple named Wendell and Monica Wilkins with a desire to move to Australia. The Wilkins quickly leave just before the Death Eater Yaxley arrives. The Hermione in the book does state that she will eventually reverse the charm once things are safe since a False Memory Charm can be lifted as demonstrated by Dumbledore, Slughorn, Shacklebolt. A Memory Charm, however, cannot. This makes Hermione's plight in the film much more darker and compelling. Also, the dance scene between her and Harry was written exclusively for the film and was not in the book.
10) The Deadly Hallows Part 2 - Battle of Hogwarts scene pays homage to previous films
In the final film, there is a scene from the Battle of Hogwarts, where Harry, Ron and Hermione are running through the castle's courtyard. First they encounter a giant ogre which resembles the troll from the girls' toilet in the first film. Next, they meet some giant spiders just the ones Harry and Ron face in the second film. Then, the trio clash with a werewolf attacking Lavender Brown, which reminds us of Professor Lupin's dark side in the third book. Then, the three friends are faced with a gang of Dementors like the ones Harry had to fight of in the fifth film. Finally, we witness the Half Blood Prince being murdered by his Dark Lord and we get to look into his memories, just like in the sixth film. In just two minutes, Harry and his two best friends easily pass through deadly foes that were once too difficult for them to face, showing that our heroic trio have truly grown up and matured through the series from young Hogwarts students into full-fledged Wizards.