A man was walking along the sidewalk with his dog on one of those retractable leashes.  The man suddenly moved toward the right to drop something in a waste container;  dog continued in a straight line, its leash extending across sidewalk;  a youth on a skateboard was in a whiz down the pavement toward them.  Man, in an instant, raised the leash;   youth, in an instant, ducked under the ascending leash;  dog plodded steadily on.