1. The first Harry Potter book was published in 1998, the same year the final Battle of Hogwarts was fought. Says Rowling, “I open at the close.”
2. An inscription on the Mirror of Erised reads “I show not your face but your heart’s desire” when reflected in a mirror.
3. “Expecto Patronum” literally translates to “I await a guardian” in Latin.
4. And because the Patronus is a physical representation of one’s soul, James Potter’s stag and Lily Potter’s doe make them literal soulmates.
5. Ron’s Patronus is a Jack Russell terrier, known for chasing otters. Hermione’s is, coincidentally, an otter.
6. After Fred’s death, George was never able to perform the Patronus again.
7. J.K. Rowling said she found Hedwig’s name in a book of saints.
8. When rearranged, the letters in Remus Lupin spell “primus lune,” which roughly translates to “first moon” in Latin.
9. Rowling said if Voldemort saw a boggart it would take the shape of his own corpse, since death was his greatest fear.
12. The Malfoys’ last name comes from the Latin “maleficus,” which means evil doing.
13. The Elder Wand is the only known wand to contain hair from the Thestral, a beast that can only be seen by those who have witnessed death.
14. Originally Rowling wanted to kill off Arthur Weasley in the fifth book, but switched him for Sirius Black.
15. Dementors are a physical representation of Rowling’s experience with depression.
16. Voldemort is incapable of love because he was conceived under a love potion.
17. Snape hated Neville because Neville was nearly the Chosen One. If he had been chosen, Lily wouldn’t have died so young.
18. If Muggles came upon Hogwarts, it would look like a decrepit building with a “Keep Out: Dangerous” sign on it.
19. Dementors don’t breed; they grow like fungus where there is decay.
20. The day Harry and Ron saved Hermione from the troll — the day they became friends — is the 10-year anniversary of Harry’s parents’ death.
23. Dumbledore is an Old English word for “bumblebee.” Rowling said she chose the name because she imagined Dumbledore enjoyed humming to himself.
24. Rowling said she seriously considered killing off Ron in the middle of the series.
25. In the Harry Potter universe, there are an estimated 3,000 wizards living in Great Britain.
26. Rowling made Harry wear glasses as a constant reminder of his vulnerability.
27. Most of the Blacks are named after stars. Sirius, for example, is named after the dog star.
28. Harry first arrived at 4 Privet Drive on Hagrid’s motorbike. He left for the last time the very same way.
Oops! A previous version of this post said Lily and Snape have the same last word. This was incorrect.