By Abby Ohlheiser, The Washington Post Ron Weasley’s “patronus” is a Jack Russell terrier. Moaning Myrtle’s full name is Myrtle Elizabeth Warren. Harry Potter’s uncle loves “Top Gear.” Fluffy the three-headed dog was repatriated to Greece. Tuition at Hogwarts is free. With just a tweet, J.K. Rowling can change and shape the world of Harry Potter with new, authoritative information.