"Twilight" star Kellan Lutz took over "Punk'd" (Thu., 10 p.m. ET on MTV) for the week, and immediately targeted some of his Hollywood friends. He enlisted three-time "Dancing with the Stars" champ Derek Hough to help prank his sister Julianne. The set-up was pretty simple, with Derek getting out of the car to move an obstruction, and then pretending to fall into a quagmire and get stuck.Julianne certainly fell for it, though she didn't get into the muck to try and help her brother.