Oops , she did it again . Some fans of Britney Spears are accusing the singer of lip-syncing to her song `` Perfume '' during her Las Vegas show . According to gossip site Oh No They Did n't , Spears ' mouth is moving but the audience is mostly hearing singer Sia 's version of the track . Billboard points out that Sia -- best known for her hit song `` Chandelier '' -- is credited as one of the writers of `` Perfume . '' An acoustic version of the song as performed by Sia is big on YouTube . `` If you listen closely to the performance video , you can make out some of Spears ' vocals under Sia 's more charactered voice , '' Colin Stutz writes for Billboard . `` That 's because , most likely , Spears uses Sia 's track as an in-monitor guide when she sings . Only this time it was put into the house mix , making for an embarrassing accident . '' It 's not the first time Spears has been called out for the vocalizations during her Vegas show , which is part of a two-year residency . In reviewing the show for the Los Angeles Times , writer Mikael Wood points out that the singer 's show appears to take its title , `` Piece of Me , '' literally . `` Whatever the scale of the number ... the singer 's presence felt so diminished -- her dancing a tentative shadow of what it used to be , her vocals apparently lip-synced for the majority of the show -- as if to make the production 's title seem a taunt , '' Wood writes . While her manager Adam Leber initially denied that Spears was n't singing live during the show , he later backtracked during an interview with Medium.com . `` To put on the show that she puts on , it 's virtually impossible to sing the entire time and do what she does , '' he said . `` She 's singing on every song , basically , when she has the ability to sing . There 's no way you can dance for 90 minutes straight and sing the entire time . ''
Billboard says you can hears Spears singing under vocals . Track is reportedly of singer / songwriter vocals . Billboard backtracked on saying Spears sings live .