Value of Repetition, Part 12 (Mixture of Elements)
John Lee Hooker's "Boom Boom" uses the same device as Slim Harpo's "Baby Scratch My Back"... the main lick happens before the bar, with the final note landing on the downbeat of the bar. There are two more cool elements in "Boom Boom"...
1) The main lick only changes it's resolution note, to match the chord change.
2) There's a call-and-response happening. In the opening, the band responds to the main lick on the guitar. When the vocals enter, the band and guitar play the main lick and they go back and forth.
Pretty cool of use of chord anticipation, chord tones, repetitive phrasing and mixture of consistency and change to make things both understandable and interesting at the same time.