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

Mover over Perry, the scruffy Inside Llewyn Davis star will take it from here

Listen: Katy Perry's 'Birthday'

Get ready to memorize this gleeful ditty and then urge someone you love to 'let me get you in your birthday suit...' …

By Editors

Musto on the Gaga vs. Katy Showdown

Plus: 'Hugh Jackman Is Straight' and Other Hot Gossip Tidbits

By Michael Musto