Yo-Yo Ma to the Rescue

Yo-Yo and Aidan

Returning from a spring break trip to Montana, my 14-year-old son Aidan and I were minding our own business, walking among the weary hordes of travelers at the Chicago airport. Then we noticed a slight commotion twenty feet ahead of us. A middle-aged woman had accidentally dropped her boarding pass, but since she wore an iPod, she was unable to hear the voices of people calling out. So the woman strode  briskly on, unaware.

Behind her, about a dozen people were doing what...