I’m guessing you’ve seen this before: A young kid shouting or singing through a cardboard paper-towel roll, projecting his voice through the house, when the inevitable happens. He slips over to his little sister, holds the make-shift megaphone to her ear, and, just for fun, yells at the top of his lungs. Sister cries, mom or dad rushes in, paper-towel roll goes in the garbage. In our individual...