Britney Spears has unleashed some footage of herself dancing

Britney Spears has popped another teaser video thing for her forth­com­ing doc­u­ment­ary and Vegas residency onto the world wide web.

This one shows the 'Like a Virgin/Hollywood Medley' chanteuse rehears­ing dance moves with her new cho­reo­grapher intercut with bits of chat about how hard it's all been.

Fans of her signature hair-flip dance move are advised to skip to 1:12.