Paul McCartney and Katy Perry are buds who swap songwriting tips!

Paul McCartney and Katy Perry are buds who swap songwriting tips!
Katy Perry arrives to the world premiere of "The Smurfs 2" at the Regency Village Theatre on Sunday, July 28, 2013 in Los Angeles. (Photo by John Shearer/Invision/AP)
LONDON (AP) — Even a star who has been performing for more than 50 years sometimes wants a do-over.

Sir Paul McCartney sang his new song "New" at a taping of "The Graham Norton Show" in London on Thursday — then decided he wanted a second take. The former Beatle's instincts were right on target: round two had much more verve.

McCartney and pop princess Katy Perry also gave a master class in songwriting at the taping. McCartney says he and late writing partner John Lennon expected to come away with a song every time they brainstormed. Perry, who says she's "an observer of life," carries around a recorder to stash away phrases that strike her fancy.

McCartney later treated the audience to a rousing song not on his new album: "Lady Madonna."