As far as i know it's just 'tapping', it's when you kind of play the strings with the tips of your fingers at the high part of the neck. It, in my experience, enables you to use real speed...i just haven't got the other hand to match it
He used it alot, interestingly thats why his signiture bass( if your into details lol), the buzzard, has such a high upper body - so he could rest his elbow while tapping.
In essence, it's just like typing. (i think!)
