A good visual for that exercise is to skip the rubber knife; give your friend a marker. Pretend that's a knife and try to disarm him. When you're done, count

A good visual for that exercise is to skip the rubber knife; give your friend a marker. Pretend that's a knife and try to disarm him. When you're done, count up the marks and see how many times you'd have been cut and where. Even without taking into account the edge of the fictional knife, it's a pretty damning visual. (Also: with a standard rubber knife, too many of the hits during the exercise won't be noticed or remembered by either party.)