The café has a promotional poster for Equus on the wall. It's hard to see in the movie itself, but visible in the special features.
This is not the first time Alan Rickman had been romantic with Geraldine Somerville, if one watches the film Close My Eyes.
Actor-Inspired Element: For the scene where we get to see Hermione's bedroom, Emma Watson told the set department to add more books. They obliged.
Adaptational Context Change: The interrupted kiss in the book is a minor Tear Jerker, as Ron intentionally breaks it up in anger. In the film it's played for comedy, with George walking in on them (and actually trying to keep quiet).
Billing Displacement: Michael Gambon received extremely high billing, despite only appearing in one scene towards the end.
Deleted Role: Stanislav Ianevski filmed scenes at the wedding as Viktor Krum. They ended up on the cutting room floor. Production stills show him dancing with Emma Watson.
Fake Brit: Sort of. Kelly Macdonald is Scottish and adopts an I Am Very British accent for Helena Ravenclaw. Oddly enough Rowena Ravenclaw is described as "fair Ravenclaw from Glen", implying she was Scottish.
Fake Irish: Welsh actor Rhys Ifans does an Irish accent for Xenophilius Lovegood. His nationality is not mentioned in the books (and the audio books give him an English accent), but Evanna Lynch's Irish portrayal of Luna is so accepted that her father becomes Irish too.
Most people guessed beforehand who R.A.B. was, Sirius' brother Regulus Black, with some even correctly guessing his middle name Arcturus, from his grandfather on the Black Family Tree.
Notably, Emerson (from MuggleNet) and Melissa (from The Leaky Cauldron) were given the opportunity to interview Rowling the day after the book was released, immediately after their first read through. They both guessed R.A.B.'s identity immediately.
Tara Gilesbie, of all people, correctly guessed Harry being a Horcrux and having to commit suicide to kill Voldemort.
Method Acting: In order to play Hermione impersonating Bellatrix, Helena Bonham Carter watched Emma Watson act out the scene first and then copied what she did.
Sort of. Warwick Davis plays Griphook in this film, replacing Verne Troyer from the first film. But Davis had provided the voice in the first film, dubbing Troyer (who is American).
Nina Young played the Grey Lady in the first film. Now Kelly Macdonald plays her for her only speaking part.
Aberforth was played by an extra in the fifth film. Ciaran Hinds replaces him here.
A minor example. Mafalda Hopkirk's voice was provided by Jessica Hynes in the fifth film. She physically appears here played by Sophie Thompson. However, Emma Watson still provides the voice (as we only hear Mafalda speak while Hermione is impersonating her).
Pandering to the Base: Allegedly, the reason Umbridge was put in the book was this - to watch her get mocked even more.
Playing Gertrude: Daniel Radcliff, Emma Watson and Rupert Grint in the epilogue.
The famous 'awkward Voldemort hug' was ad-libbed by Ralph Fiennes on set. Tom Felton was genuinely weirded out.
Evanna Lynch came up with Luna's eccentric dancing at the wedding herself.
Nick Moran ad-libbed Scabior's violent twist in the air when Bellatrix attacks him with her whip. Although the filmmakers loved it, Moran ended up having to repeat the stunt for several takes.
Helena Bonham Carter and Emma Watson came up with the idea of Bellatrix carving 'Mudblood' into Hermione's arm on the spur of the moment, and it was put in.
Trolling Creator: Leading up the book's release, Rolling kept hinting that she may Torch the Franchise and Run by killing Harry so that no sequel books could be written about him. Which she did, but not permanently.
A lot of material released after the book's release (such as the trio's lives after Hogwarts) were trivia Rowling would've liked to include in the actual book.
A scene was filmed for Part I where Tonks tells Molly she's pregnant, but it was cut for time. In a Freeze-Frame Bonus you can see her wearing a maternity gown at Bill and Fleur's wedding.
A deleted scene for Deathly Hallows: Part II would've shown Hagrid fighting the Death Eaters and ultimately being captured by them; as this was removed, Hagrid's first appearance is simply him already captured.
There was serious consideration for filming the deaths of Lupin and Tonks. Also the two were originally slated to survive the books, but JK Rowling killed them off after deciding not to kill off Arthur in the fifth book.
Producers tried to change Minerva's duel with Snape to happening with Harry instead. JK Rowling had to step in, insisting the duel was an essential part of Minerva's character.
Kate Winslet was going to be offered the role of Helena Ravenclaw, but her agent rejected it before she had even considered it. This marks the second franchise Winslet narrowly missed out on (having nearly played Sauron in The Lord of the Rings). She would eventually get to be part of a franchise with Divergent.
A scene during the final battle was filmed where Draco would toss Harry his wand after he reveals that he's alive to Voldemort.
The epilogue had to be re-shot because the aging make-up on Daniel Radcliffe, Emma Watson, Rupert Grint, Bonnie Wright and Tom Felton didn't look good in the footage. Photos exist showing drastically different costumes and hairstyles for the actors.
Working titles for the book were Harry Potter and the Elder Wand and Harry Potter and the Peverell Quest. The latter was rejected for being way too cheesy, but the former would have made a lot more sense, especially since the other Hallows (the Resurrection Stone and the Invisibility Cloak) aren't really important to the story the way the Wand is, except in the thematic sense. The Stone is only discovered towards the end and put to use exactly once, and while the Cloak sees a fair amount of use, it's nothing that Harry hasn't done before, and it isn't over-used. Though it must be noted that Harry only uses the Elder Wand once, to repair his original holly-phoenix feather one.
Rowling knew straight away that she would have to kill off a member of the Weasley family but didn't know which one. Arthur was slated to die in the fifth book but got a reprieve. Ron very nearly got killed off too, when Rowling was "in a very bad place". Ultimately it was Fred who got killed.