1. When filming Harry Potter and the Prisoner of Azkaban, the pockets of Tom Felton’s (Draco Malfoy) Hogwarts robes were sewn shut to stop him from sneaking food on set.
2. When Fred and George Weasley bewitched snowballs to hit professor Quirrel’s turban, they were unwillingly hitting Voldemort in the face.
3. The first Harry Potter book was published in 1998, the same year the final Battle of Hogwarts was fought. J.K. Rowling has said, “I open at the close”.
4. In Prisoner of Azkaban, Trelawney refuses to sit at a table with 12 characters because she would be the 13th one and the first one to get up after that would die. In Order of Phoenix, 13 members of the order are sitting and Sirius is the first one to stand.
5. J.K. Rowling said that if Voldemort saw a boggart it would embody his own corpse since, death was always his greatest fear.
6. In order to fill the shops in Diagon Alley, the set crew had to go to antique shops, auctions and flea markets in the city and countryside. They were told not to tell why they needed so many jars, books or owl cages. One crew member who was buying a large number of brooms told the shopkeeper it was because she had a lot of sweeping to do.
7. Dumbledore is an old English word for ‘Bumblebee’. J.K.Rowling said she chose the name because she pictured Dumbledore humming to himself.
(References from the book J.K. Rowling’s Wizarding World Movie Magic and website https://www.independent.co.uk/arts-entertainment/books/features/20-facts-ardent-harry-potter-fans-should-know-9831152.html . )