Victor Wooten is one of the great masters of several techniques, and he uses them in his playing flawlessly. One of these is the usefull "double thumbing" technique. Watching someone do this technique is very deceiving, because it like looks a lot less and easier than it actually is. If you can slap already, then you're halfway there. All this does, is allow you to "double" your thumb time. He uses and explains this concept on the video "Victor Wooten, Live at Bass Day 98".

To start out, just slap out quater notes of E.