A stinger

Melly was running around out back tonight after dinner.  She got a little carried away and fell and scraped her elbow.  She came crying to me and I inspected the wound and kissed it better.  She asked if it was bleeding and I told her no, that it was just a "stinger" (in other words a hard hit that stings for a little while).  In tears she responded, "Dad, why does the ground have stingers on it?"