Watch the E-Shake online guitar lesson by Freekbass from 50 Freekbass Licks You MUST Know
Starting with a thump on the 1 on my low E, I then pluck a descending fill on my G string, similar to what a snare drum fill would be. In other words, my thumb is the kick drum, and my index finger/plucking finger is the snare drum. At the same time between each "snare-hit", I am using my whole right hand to create additional rhythms by striking against the body of the bass in a similar way you will see acoustic guitar players do sometimes.
The finished result is kind of giving almost a rim shot feel before each note.