Hi, I'm John Green. Welcome to my salon. This is Mental Floss on YouTube.

And did you know that in 2005 a doctor conducted a study to see if children had fewer trips to the emergency room immediately after Harry Potter books were released? And he was right.

In the weekends after The Order of the Phoenix and The Half-Blood Prince were released, there were half the amount of children at the E.R. in John Radcliffe Hospital compared with weekends directly before. It probably had something to do with the fact that, you know, they were all sitting on the couch reading all weekend rather than getting into trouble.

And that's the first of many facts about Harry Potter that I'm going to share with you today in this video brought to you by our friends at Geico. It's going to get very spoilery in here, so only watch this if you've read the books and seen the movies. Or if you never plan on doing either, in which case you're making a terrible mistake. Or if you will read the books but reading things without knowing everything that's going to happen stresses you out.

Okay, let's start with the books and move on to the movies. So the idea for Harry Potter came to J.K. Rowling when her train was delayed for four hours and the long wait gave her the right amount of time to develop the idea, you know, "Wizard school."

As you've probably heard, Rowling's manuscript got rejected about five times before it was finally published. The main complaint was that it was too long for children.

I don't know what the problem is. The books actually seem quite small to me.

But of course it did get published, so let's talk about it.

J.K. Rowling and Harry Potter share the same birthday, July 31.

But that's not the only similarity she shares with a character. Rowling's favorite character is the otter, and that, of course, is Hermione's Patronus. Interestingly, Ron's Patronus is a Jack Russell Terrier, a breed of dog that likes to chase otters.

Rowling based the Dementors in Harry Potter on her experience with depression. She's described depression as the, quote, "Cold absence of feeling," which is how Dementors are presented.

In a 1999 interview for People magazine, Rowling announced that the last word of the series was going to be "scar." But the last word of Harry Potter and the Deathly Hallows is actually "well," which gives me hope for a Book Eight.

The love potion Amortentia smells different to everyone, depending on what they like. In the book, Hermione won't say out loud the third thing she smells in the potion, but Rowling has claimed that it's Ron's hair.

To me, that potion would smell like Ron Swanson. Whiskey, sawdust and breakfast food.

Many fans, including myself, do not understand why Hedwig had to die. But according to Rowling, the loss of Hedwig represented a loss of innocence and security. She has been almost like a cuddly toy to Harry at times. Voldemort killing her marked the end of childhood.

Well yeah, but I don't want childhood to end, J.K. Rowling.

"Expecto Patronum" is Latin for "I await a protector." And that's not the only Latin phrase you can find in the series. Like Bellatrix, as in Bellatrix Lestrange, means "Female warrior." It makes sense, considering that Rowling was a classics major.

Speaking of names, Rowling found a lot of bizarre plant names for the series in a 17th Century book about herbs titled Culpepper's Complete Herbal.

Originally, Arthur Weasley was going to die at the end of The Order of the Phoenix, but then Sirius Black took his place, leaving Weasley to survive... to see one of his sons die and another lose an ear.

Stephen King once described Dolores Umbridge as the greatest make-believe villain to come along since Hannibal Lecter. And coming from someone who wrote about an evil car, that is high praise.

The driver and conductor of The Knight Bus, Stanley and Ernie, were named after Rowling's grandfathers.

J.K. Rowling is the first person ever to become a billionaire for book writing, and also the first book-writing billionaire ever to cease to be a billionaire by giving away so much money to charity.

All right, let's move on to the movies. Back in 2000, when Harry Potter and the Sorcerer's Stone was being cast, Frankie Muniz and Haley Joel Osment were rumored to be in the running for the part of Harry.

Steven Spielberg wasn't interested in making the films. He said, I purposely didn't do the Harry Potter movie because for me, that was shooting ducks in a barrel. It's just a slam-dunk. It's just like withdrawing a billion dollars and putting it into your personal bank account. 

So instead, he and Haley Joel Osment went off and made AI, and that didn't put a billion dollars in anybody's personal bank accounts.

When Rupert Grint auditioned for the films, he attempted to stand out by performing a rap.

Another person who auditioned for Ron? Tom Felton. He actually tried out for both Harry and Ron before getting cast as Malfoy.

As happens whenever you get a large group of children together, there was an outbreak of lice during the filming of The Chamber of Secrets.

And when they weren't getting lice, the kids would sneak candy onto the set. The robe pockets were so big that child actors would stick sweets and even drinks in them. Tom Felton takes credit for starting this trend, so he's to blame for the pockets eventually getting sewn shut by the wardrobe department.

Shirley Henderson, the actress who played the 14-year-old Moaning Myrtle, was 36 while filming The Chamber of Secrets. 

The Moaning Myrtles, by the way, is the name of one of my very favorite wizard rock bands. Other standout wizard rock artists include Draco and the Malfoys, Harry and the Potters, and The Whomping Willows.

Before the Deathly Hallows book was released, J.K. Rowling gave Alan Rickman some hints about Snape's true feelings so that he could properly play the character. This sometimes caused confusion on set when a director would ask Alan to do something and he would respond, "No, no, no, I can't do that. I know what is going to happen and you don't."

In the end credits of The Goblet of Fire, there's a note that reads, "No dragons were harmed in the making of this movie."

And finally, I return to my salon to tell you that Prisoner of Azkaban director Alfonso Cuarón asked Emma, Rupert and Daniel to write essays about their characters. Emma turned in a 16-page essay, Daniel's was one page long, and Rupert never turned it in at all. 

Thanks for watching this video of Mental Floss on YouTube, which was brought to you by our friends at Geico and made with the help of all of these nice people. Don't forget to watch our other shows, and as we say in my hometown, don't forget to be awesome.