A body handle is a different way of applying a morph to something - instead of a dial, you have a little glowing ball, or something that shows up in preview but doesn't render. This can be selected and moved around, giving more control than a straight morph dial. It actually works by having a non-existent "ghost" body part that's named so it doesn't conform to anything, but once selected influences its parent part in the same way that real limbs do.