Pop star talks to David Letterman about her diagnosis
                                
                                
                                    (Newser) -
                                    At one point during her interview with David Letterman for his Netflix series, Billie Eilish turned her head and opened her mouth, and Letterman jokingly asked if she'd seen a fly, per  TheNews.com . "No, I'm ticcing," replied Eilish, referring to the tics she has because...