Katy Perry taped background vocals for 'Ooh La La' Actress Katy Perry attends the premiere of the motion picture animated comedy "The Smurfs 2" at the Regency Village Theatre in the Westwood section of Los Angeles on July 28, 2013. The Smurfs join forces with their human friends to rescue Smurfette who has been kidnapped. LOS ANGELES, July 29 (UPI) -- U.S. pop star Katy Perry says she sang in the background of Britney Spears' "Smurfs 2" song "Ooh La La!" The single was written by Perry's frequent collaborator Bonnie McKee. It can be heard playing over the end credits of the "Smurfs 2" family movie. "Me and Bonnie secretly did some background vocals on that song," Perry told E! So maybe listen for our voices.