If not little known, at least little remembered. ;) I've collected here eleven (in my opinion) of the most interesting and useful ones. Plus my comments on some of them.~ ~ ~ ~ ~There is no such thing as a pureblood family. Every wizarding family has a muggle or a few among them. Some just choose to cross them over in their family tree and pretend they don't exist and instead claim themselves as purebloods.Wizards and witches have a much longer life expectancy than muggles. Dumbledore is 150 years old and McGonagall is sprightly 70-years old.Hogwarts does not accept foreigners but serves only Britain and Ireland.There's a magic potion for developing photographs and it's that potion that makes the photos also move.A Squib child can be born to any witch or a wizard regardless of how pure the blood. The other of the parents can be even a muggle. Still Squibs are rare because magic is a dominant and resilient gene.Most magical children are being home schooled but some may go to a muggles' primary school before Hogwarts. Purity of blood is irrelevant in this matter.-- link with references to Rowling's official wordsFred and George did not pay attention to Peter Pettigrew on the Marauders' Map because they hadn't heard the story of Peter and Sirius and even if they had, they'd have no reason to think that one is the man murdered years ago. Plus, they used the Map for their own mischief and thus focused on only the places they needed to. And finally, you must remember there were hundreds of little dots moving on the Map at any given time and the twins did not know all the students by the name.Was Snape hiding under the Invisibility Cloak on the night the Potters died? No, he wasn't.The Lestranges did not know about the Prophecy.It's very rare (but possible) that magic shows in a person late in life instead of in their childhood. Almost always it shows in a person before age 11.No one knows where magic comes from.