 The song 's structure differs from a well @-@ defined twelve @-@ bar blues . The verses are not consistent and range from fourteen to fifteen bars in length . Additionally , the harmonic progression is often implied rather than stated ( full IV and V chords are not used ) . Johnson uses a Spanish or open G tuning with the guitar tuned up to the key of B. This facilitates Johnson 's use of a slide , which features as prominently in the song as the vocal . The slide parts function more as a second " answer " vocal than accompaniment , with the tension underscoring the dark turmoil of the lyrics . Charters characterizes the song 's rhythm as ambiguous , imparting both a 44 and 88 feel . Music writer Dave Headlam elaborates on Johnson 's rhythm : 
