J.K. Rowling has posted the latest of 12 new Harry Potter "moments" on her website, Pottermore.
Update: Here's the sixth riddle.
Spoiler: The riddle reveals new writing in which Rowling explains she originally intended to have a vampire teacher at Hogwarts.
Although vampires exist in the world of Harry Potter, as shown by the literature that Harry and his friends study in Defence Against the Dark Arts, they play no meaningful part in the story.
Looking back through my earliest notebooks, however, I found that on my very earliest list of staff, there was a subjectless vampire teacher I had forgotten, called "Trocar".
Evidently I did not think much of him as a character, though, because he disappears fairly early on in my notes.
For a long time there was a persistent fan rumour that Snape might be a vampire. While it's true that he has an unhealthy pallor, no corpses with puncture marks in their necks ever turn up at Hogwarts.
You can read the whole thing by logging into Pottermore, and solving the riddle.
The fourth and fifth days led to no new info, but solving the riddle on day three revealed why Rowling made Snape Potions Master:
Chemistry was my least favourite subject at school, and I gave it up as soon as I could. Naturally when I was trying to decide which subject Harry's arch-enemy, Severus Snape, should teach, it had to be the wizarding equivalent. This makes it all the stranger that I found Snape's introduction to his subject quite compelling ('I can teach you to bottle fame, brew glory, even stopper death…'), apparently part of me found Potions quite as interesting as Snape did; and indeed I enjoyed creating potions in the books, and researching ingredients for them.
The moment also included info about cauldrons, which "are enchanted to make them lighter to carry, as they are most commonly made of pewter or iron."
The second riddle led to information about Florean Fortesque, owner of Diagon Alley's ice cream parlour.
Rowling reveals she had him kidnapped, intending him to be rescued later by Harry, but eventually cut the plot line.
I seemed to have had him kidnapped and killed for no reason. He is not the first wizard whom Voldemort murdered because he knew too much (or too little), but he is the only one I feel guilty about, because it was all my fault.