WATCH: Oscar Isaac Performs Folk Version of Katy Perry's "Roar"

While promoting Inside Llewyn Davis, star Oscar Isaac stopped by Late Night with Jimmy Fallon to discuss the Coen Brothers folk movie. Given how much Fallon loves playing music on the show, the host hands Isaac a guitar and challenges him to turn any song into a folk jam.

The actor opts for Katy Perry's hit, "Roar," to Fallon's delight. The Late Night host can't help himself and jumps in on the jam session.