We recently asked members of the BuzzFeed Community to tell us which piece of Harry Potter movie trivia totally blew their minds. Here's what they had to say...
1. Tom Felton would sneak sweets and snacks on to set in the pockets of his robes, and when he was found out they were sewn shut. – sydneyk416a6bc73
2. Before Richard Harris died, he told director Christopher Columbus that if he was recast, he would kill him. – harpstringhum
3. The train used to film scenes featuring the Hogwarts Express was vandalised between filming of Chamber of Secrets and Prisoner of Azkaban. – betz04922
4. Malfoy's "I didn't know you could read" line was improvised by director Chris Columbus. Tom Felton said it was one of his favourite moments from the series. – jessicaf48ef340eb
5. The door to the Chamber of Secrets isn't CGI: It's all mechanical, and still works to this day. – brandies427fe3094
6. Harry's wand changes between the second and third movies. – bluewater99pdc
According to Pottermore, the wand's design "evolved over the course of the films". Before filming started on Prisoner of Azkaban, director Alfonso Cuarón offered the actors a selection of new wands to choose from. Daniel Radcliffe chose Harry's famous tree trunk-esque, whittled wand, which art director Hattie Storey called "more mysterious and magical".
7. And Daniel Radcliffe went through around 80 wands during filming, because he kept wearing them out. – hannahb4059f284c
8. J.K. Rowling was offered the part of Lily Potter in the first movie's flashback scenes, but turned it down. – georgew4445ba9e8
9. The puppets used to create the Dementors were filmed underwater and then animated to produce the eerie floating effect you see in the movies. – tsat
10. Emma Watson had an on-set hamster during the filming of the first movie, but it died, so the props department made a tiny hamster-sized coffin to bury it. – tdcbri
11. Ralph Fiennes originally wore tights under his Voldemort robes, but the gusset would slip down and make it difficult to walk, so in the end he wore stockings and garters. – allisonc44498e548
13. The actress who played Moaning Myrtle was actually 36 years old at the time of filming Chamber of Secrets. – faithtan
14. The actor who plays young Voldemort in Half-Blood Prince – Hero Fiennes-Tiffin – is the nephew of Ralph Fiennes, who plays the older Voldemort. – sarah81327134
15. Not only did Daniel Radcliffe have an allergic reaction to green contact lenses, he also had an allergic reaction to the original glasses they used for Harry. – alexac442ac570d
16. Katie Leung, who played Cho Chang, listened to Coldplay in her dressing room so it was easier to start crying in scenes. – gryffindor1207
17. Dolores Umbridge's outfits are a light pink at the beginning of Order of the Phoenix, but get darker and brighter as the movies go on, because she's getting "more hysterical". – Ellie Bate
"I started with lighter pink, and then as the film developed the pinks are getting hotter and hotter and hotter because she’s getting more and more hysterical," said costume designer Jany Temime.