Sia's latest track is another cathartic ballad, with a sprinkling of piano and cavernous drums that climb to meet a soaring hook. I picked the wrong kind, she sings. Time after time I drank from the poison wine. But this is a Sia song, so things are getting better, obstacles are being surmounted: Baby you're alright, baby I've seen the light. Listen above, and find out how Sia is changing pop.