Greg Wilson walked to the bottom of the staircase and yelled for his son, Billy. "Billy, could you come here for a minute?" There was no reply, so again he yelled, this time a little louder. "Billy!" Still silence. What the hell was that boy doing? Greg wondered, and made his way up the staircase in search of his son. Billy wasn't able to hear his dad yell, for he was preoccupied listening to music with his headphones on...