"...then reach your hand into a friend's mouth and touch one of his dental fillings. Did you notice how your friend twitched violently and cried out in pain? "

If I may point out a flaw in the above experiment: What if he/she in "shock and awe" of the pain clamp down on my finger? I think it would be a lot safer if I touch elsewhere, like the tip of their nose. Though in your winters the tip of the nose may not be sensitive enough.

BTW was there really a "Bob Transformer"?