Carrie Underwood sported a flirty, punk rock look as she took the stage at Sunday's ACM Awards wearing a short black and silver number with bright pink extensions in her hair. Launching into her catchy hit, 'Undo It,' she pranced around the stage showing off her gorgeous gams with some rocking dance moves ... just as an iconic rocker joined for a surprise duet. Aerosmith's Steven Tyler was arguably the biggest surprise of the night, trading vocals with Carrie on her hit, followed by his own classic 'Walk This Way.' Watch video of their electrifying performance below.