At one end of the worm, he sets up a Neko rig that sinks headfirst. When placed elsewhere in a fairly thick body, it alters the sink rate or slightly speeds up the descent. Check the action after each addition.
The three weights available are 0.45, 0.875, and 1.75 g. Start with a light weight to see how it performs. Push the insert all the way in and check its hold after a fight; torn material holds it less securely.