J.K. Rowling has cast another spell, this time helping a young fan in a battle against the "dementors" of depression. On Sunday night, an 18-year-old fan from Brazil named Marina who uses the Twitter handle "pale emo nerd" sent out a series of increasingly distressing tweets, tagging the "Harry Potter" author in the first one: @jk_rowling could you please teach me how to scare the dementors that have been living under my bed?