We all thought Britney was lying after she told reporters that she would be singing LIVE during her stay in Las Vegas.  

While performing recently, Britney was caught missing her cue during her song, and guess what...even without the mic up to her mouth we heard her sing.  So...we could assume one of two things, 1 - Britney is great at throwing her voice.  OR 2 - She's lip-synching.  

We're gonna go with number 2.  Check out the video.  

(special thanks to samberato for posting this)