You've seen the pictures, now watch the video! Rihanna opened the Billboard Music Awards with her raunchy song "S&M" and had the help of Britney Spears, who joined the performance towards the end of the number. With lots of pole dancing, sexy moves and a pillow fight — the song is called "S&M," after all! — it was a hot start to the performance-filled evening. Britney will soon hit the stage to perform her hit "Till the World Ends" with Nicki Minaj, but first catch her duet with Rihanna now!