A couple in Arkansas had given their six-year-old son strict instructions to come home from playing every afternoon no later than 5 p.m.  He was allowed to play with his friends, but his parents were quite serious about his curfew. If not home by 5 p.m., they'd begin to worry and call around the neighborhood to find out where he was. The boy knew this, though, and was careful to arrive every day on time.

One Mar…