Double slapping is an advanced technique that involves adding a sound right before the "pluck" to give the note just a hint of percussion. On the BASS BOX this is done by striking the blade with the middle part of the finger right before the "pluck"- the "boom chuck, boom chuck" becomes "ba-boom chuck, ba-boom chuck". Alternatively, occasionally I will tap the front of the BASS BOX with the side of my thumb on the off beat, the second and fourth beat of a measure- the "boom chuck, boom chuck" becomes "boom tap, boom tap". Combining these double slap sounds, the "boom chuck, boom chuck" becomes "ba-boom tap, ba-boom tap".