8 things we just learned about the 'Harry Potter' universe from J.K. Rowling's latest e-books

During Lord Voldemort's first attempt to take over the world, Death Eaters went on random anti-Muggle killing sprees. During one of these sprees, they killed McGonagall's first love, Dougal McGregor.

McGonagall never married him because she knew it would be difficult for them to have a life together: she was a witch, he was a muggle looking forward to inheriting his dad's farm. But after his death, she wondered if she could have saved him if she married him.

Appearing on chocolate frog cards is a fairly big deal in the wizarding world. The cards are collectible items and show history's greatest wizards and their accomplishments.

It was a controversial decision. His true roll in Voldemort's demise was not widely known at first, and it's easy to see how some people might have viewed Snape as a puppet for Voldemort, especially for allowing Death Eaters to teach classes at Hogwarts.

So McGonagall consulted Harry about it. Rowling writes that McGonagall was uncommonly close to Harry not just because of their shared experiences and because his parents were two of her favorite students, "but because he, like herself, had suffered serious bereavements."

Harry. of course, said yes.

In "Short Stories From Hogwarts of Heroism, Hardship and Dangerous Hobbies," Rowling goes through the steps of how to become an Animagus, or a wizard or witch who can transform into an animal at will.

Unsurprisingly, it's really, really hard. There are ten steps to becoming an animagus. Here's the first one:

"1. For the space of one entire month (from full moon to full moon), a single leaf from a Mandrake must be carried constantly in the mouth. The leaf must not be swallowed or taken out of the mouth at any point. If the leaf is removed from the mouth, the process must be started again."

The rest of the process is similarly punishing. At the next full moon, you need to take the mandrake leaf and put it in a vial filled with your saliva, then mix it with dew "from a place that neither sunlight nor human feet have touched for a full seven days," among other ingredients. That vial has to be placed somewhere where it can absorb the rays of the full moon. If it's cloudy that night, sorry, you have to start over again.

After that, you need to wait for a specific kind of storm to come before you can proceed to step three. If it doesn't come for years, you just have to wait. You get the idea.

"Short Stories from Hogwarts: Power, Politics and Pesky Poltergeists" goes into the backstory of Horace Eugene Flaccus Slughorn, Harry's sixth-year Potions Master.

Slughorn was important because, as Tom Riddle's teacher, he told him about horcruxes and therefore might have helped him become immortal.

After Voldemort's fall, Slughorn was relieved. If Voldemort was really dead, he reasoned, then he couldn't have made horcruxes.

Nonetheless, "it was Slughorn’s extremity of relief, and the disjointed phrases he let fall in the first rush of emotion after hearing of Voldemort’s defeat, that first alerted Dumbledore to the possibility that Slughorn had shared Dark secrets with Tom Riddle," Rowling writes. Dumbledore tried to question him, and Slughorn clammed up, then quit his teaching job after 50 years at Hogwarts.

After Harry returned from the Triwizard Tournament in "Harry Potter and the Goblet of Fire" saying that Voldemort was back, the Ministry dismissed him.

But Slughorn believed Harry. Three nights after Cedric Diggory's death, the Death Eater Corban Yaxley "arrived at Slughorn’s house under cover of night, clearly intending to recruit him, or take him by force to Voldemort."

Slughorn went on the run, hiding in muggles' houses and evading the Death Eaters until Dumbledore found him and, with Harry, persuaded him to return to Hogwarts for Harry's sixth year.

Slughorn was a Slytherin, the Hogwarts house commonly considered to be the "bad guys" in Rowling's world. But Slughorn complicated the moral guidelines of the "Harry Potter" universe.

As Rowling writes, "Slughorn’s genuine remorse for the damage he had done in telling Riddle what he wanted to know is conclusive proof that he is not, and never was, Death Eater material. A little weak, a little lazy, and certainly snobbish, Slughorn is nevertheless kind-hearted, with a fully functional conscience."

During the Battle of Hogwarts, Slughorn — along with Minerva McGonagall and Kingsley Shacklebolt — was one of the last three to duel Voldemort before Voldemort battled Harry. His courage, along with that of Regulus Black, "removed much of the stigma that had been attached to Slytherin house for hundreds of years past."

Now his portrait has a place of honor in the Slytherin common room.