This was influenced by a song of the same name recorded by Blues great Sonny Boy Williamson and written by Willie Dixon. The Dixon composition was so similar that Led Zeppelin reached a settlement with Dixon over the royalties for the song, and credited Dixon as the writer when this appeared on Led Zeppelin's How The West Was Won live DVD.
Led Zeppelin frequently performed this live, with interplay between Jimmy Page's guitar, John Bonham's drums and John Paul Jones' bass. This can be heard on CD 3 of How The West Was Won. (thanks, Adrian - Wilmington, DE)
The battle between Bonham and Page was referred to as a completely separate song entitled "Bring It On Back" when done live. (thanks, Chris - Whitesboro, NY)
The harmonica part was recorded in Vancouver. The band went on tour with the master tapes from Led Zeppelin II and now and then stopped into a studio to record parts. (thanks, Dean - Vancouver, Canada)
On Led Zeppelin's 1973 US tour, they played part of this as an intro to "Black Dog." (thanks, Bertrand - Paris, France)
