Why is Luna Lovegood reading this book upside-down?
He flicked through the rest of the magazine. Pausing every few pages he read an accusation that the Tutshill Tornados were winning the Quidditch League by a combination of blackmail, illegal broom-tampering, and torture; an interview with a wizard who claimed to have flown to the moon on a Cleansweep Six and brought back a bag of moon frogs to prove it; and an article on ancient runes, which at least explained why Luna had been reading The Quibbler upside down. According to the magazine, if you turned the runes on their heads they revealed a spell to make your enemy’s ears turn into kumquats. In fact, compared to the rest of the articles in The Quibbler, the suggestion that Sirius might really be the lead singer of The Hobgoblins was quite sensible.
Harry Potter and the Order of the Phoenix, chapter 10: "Luna Lovegood" (emphasis added)