Howard, the Alabama Shakes frontwoman, steps into Jack White's Third Man Records lab to take on "I Wonder," a Vietnam-era tune by Seventies sugar-man Rodriguez. Backed by one of White's touring bands, she and soul singer Ruby Amanfu turn in a sisterly workout with a reggae breakdown – what Bonnie Raitt might sound like if she went through a down-home garage-rock phase.

Click to listen to Brittany Howard & Ruby Amanfu's 'I Wonder'

“The Pretender”

This song wasn't part of the planned track listing for 2007's Echoes, Silence, Patience & Grace, and was put together in a day. "It happened after we recorded a lot of stuff," said Dave Grohl. Yet it ended up as the album opener and the lead single. Grohl called it "a stomping Foo Fighters uptempo song with a little bit of Chuck Berry in it." The singer hinted at the lyrics' political overtones: "Everyone's been f---ed over before and I think a lot of people feel f---ed over right now and they're not getting what they were promised."