Kacey Musgraves and Katy Perry Harmonize on 'Keep It to Yourself'

While it's a little odd to see the bewitching Katy Perry as a backup singer, her low harmonies on Kacey Musgraves' "Keep It to Yourself" make for a captivating version of the hit song. The two performed together for CMT Crossroads earlier this summer, trading lines on each other's tunes, but "Keep It to Yourself" didn't make the televised broadcast.

What did make the cut for the show's 50th episode were the country star's sassy "Step Off" and Grammy-winning "Merry Go Round," along with the pop star's colossal hits, "Roar" and "Teenage Dream." "Follow Your Arrow" was a particularly poignant performance,......