Oh that - well he ripped that "trick" off bach (like most of his other tricks) - go check my toccata and fuge - it encapsulates alot of it (i did it with tapping, but it can be played without aswell if you alter the shape on the fretboard a bit. This "Organpoint" technique is one of the techniques used in counterpointed music - the name is derrived from organs with footmanuals (now that term is pretty sick *LOL*)- which are pretty much a keyboard for the feet (you can see that on hammond organs aswell) - where you hold a note whilst playing a melody on top of it.