1. Hermione's name was almost "Hermione Puckle".
It has a sour tone to it, right? J.K Rowling thought so too and changed it to something that suited the character better. Hermione was also going to have a younger sister but Rowling never found the right moment to stick her in the books.
2. Hedwig, Harry's Snowy Owl, isn't entirely accurate.
It was during the writing of book two that J.K Rowling realized that Snowy Owls are silent, meaning that Hedwig’s knowing hoots and conversational noises weren’t quite true-to-life. She admits this was just a research hole on her part, but says readers should feel free to assume that her unusual talents are just part of her magical ability. Incidentally, although Hedwig is female, she is played by a male in the movies because females aren’t wholly white like males are.
3. Collecting unusual names and words has been a lifelong habit for Rowling.
She has said that she loves reading lists of them, from war memorials to baby name books, and made it a point to remember her favorites. Some of them found a new home in the Harry Potter books. She makes up some of the words too – “quidditch” is a Rowling original. She filled up five pages of made-up words that started with “Q” before she hit on one that sounded right. “Voldemort” and “Malfoy” were also invented.
4. Fred and George Weasely were born on April Fools' Day.
Go figure. While we’re talking about the Weasleys, there was a Weasley cousin named Mafalda who got edited out of The Goblet of Fire in order to make room for the love-to-hate-her invasive “journalist” Rita Skeeter. That’s probably best – Ginny Weasley is supposed to have been the first girl born to the Weasley family for several generations, so scrapping Malfalda supports that backstory.
5. Snape was partially based on a teacher J.K Rowling once had.
She likes to write to him though, because she finds him such a pathetic creature.