1. Daniel Radcliffe auditioned for the role of Harry Potter after he was approached by producer David Heyman. Heyman spotted Radcliffe on a trip to the theatre with his father — who Heyman knew — and immediately felt he had to play Harry. The producer set up a meeting the following day.
2. Radcliffe first heard he had got the part when he was in the bath. His dad answered the phone and told him the news later.
3. The next morning he woke up at 2am thinking it had been a dream.
5. Rupert Grint became Ron Weasley after he saw a casting call on Newsround. In his audition tape, he dressed up as his female drama teacher and performed a short rap about how much he wanted to be in the film.
7. She was halfway through reading the third book when she first auditioned.
8. And the audition took place in the school gym.
9. In total, she auditioned five times.
10. Radcliffe was the last of the three lead actors to be cast.
11. And J.K. Rowling has said that watching his audition tape was like "watching a son".
12. At one point in the casting process, Radcliffe, Grint, and Watson all auditioned together.
13. Rowling spoke to Watson on the phone before they met, and said she fell in love. And so, when they met IRL and Rowling realised that Watson was more beautiful than she had imagined Hermione, she was OK with it.
14. Similarly, when Tanya Seghatchian, the film's executive producer, first saw Watson's screen test she wrote in her notebook: "Perfect! But she is rather beautiful."
15. Rowling has since said that Radcliffe, Grint, and Watson were all too good-looking for their parts.
16. But she said that Devon Murray looked exactly as she imagined Seamus Finnigan.
17. At first, producers wanted to combine two or three of the books into one film.
18. They also talked about making an animated film instead.
19. Rowling specifically requested that the film's entire cast should be British (although Griphook was played by Verne Troyer, with Warwick Davis as his voice).
20. She also insisted on having final approval of the script.
22. When production designer Stuart Craig asked Rowling about the geography of Hogwarts, she drew a map on an A4 piece of paper for him. Ten years later, while working on the eighth film, he still referred to it.
23. Rowling has said that the one actor she wanted the most was Robbie Coltrane as Hagrid. She said that not having him on board would have been a deal-breaker.
24. Robin Williams was turned down for the role of Hagrid.
25. And Tim Roth turned down the role of Snape.
26. Rik Mayall was cast as Peeves the Poltergeist and filmed for three weeks. He was eventually cut from the film.
27. Every child who worked on the film, including those who were doubles and stand-ins, went to school on set.
28. They each had between three and five hours of one-to-one tuition every day.
29. But they never got any homework.
30. Because they were so young, Radcliffe, Grint, and Watson were only allowed on site for nine hours a day. They had to be given an hour for lunch and they had to take 15-minute breaks every hour. In total, that meant that they each filmed for no longer than four and a half hours a day.
31. They were also banned from skiing throughout the duration of the films.
32. Actress Hatty Jones almost played Hermione.
34. Richard Harris initially turned down the part of Dumbledore. He ended up taking it because his granddaughter convinced him to.
35. Rowling was offered the chance to play Lily Potter in the Mirror of Erised scenes, but she turned it down.
36. When Grint was cast, he said he could relate to Ron because he too has lots of hand-me-downs. But Grint's brother is actually younger than him; he's just bigger.
37. Grint kept a broken piece of the horse from the giant Wizard's Chess set.
38. As a 12-year-old, Emma Watson fancied Tom Felton.
39. Before Radcliffe was cast, his dad read him the first two books.
40. He did a great Basilisk voice.
43. Lots of the owls were also digitally created.
44. Two different versions of Hagrid's hut were built: One was massive and contained only large props so that the actors would look small inside it, and the other was normal-sized so Hagrid would look really big inside it.
46. In the first cut of the film, there was a scene in which Hagrid and Harry get the tube together. It was later deleted.
47. Although many buildings were used for filming Hogwarts, Gloucester Cathedral was the main one.
48. Lacock Abbey, Whitby Abbey, and Durham Cathedral were also used.
49. And the dining hall of Christ Church college at Oxford University was used for the Great Hall.
50. The last scene of the film was shot on the first day.
51. At first, Radcliffe was made to wear green contact lenses so his eyes would match Harry's. However, he had a severe allergic reaction to them.
52. He was also allergic to his glasses. They gave him whiteheads around his eyes.
53. And Watson was supposed to wear buck teeth. However, producers decided against it because she couldn't talk with them in.
54. One day, Radcliffe and Grint stole Robbie Coltrane's mobile phone and set its language to Turkish.
55. On another occasion, Watson printed out two signs saying "kick me" and stuck them on Radcliffe and Grint's backs. It took them 20 minutes to notice.
56. The trio were also caught breaking a book from the set on camera and then pretending it didn't happen.
57. If you look carefully, you can see Watson mouthing Radcliffe and Grint's lines along with them because she learned them all.
58. Watson's favourite Hermione line from all of the films was, "Now if you two don't mind, I'm going to bed before either of you come up with another clever idea to get us killed – or worse, expelled."