An Old Man, riding on his Ass,   Had found a spot of thrifty grass,
  And there turn'd loose his weary beast.
  Old Grizzle, pleased with such a feast,
  Flung up his heels, and caper'd round,
  Then roll'd and rubb'd upon the ground,
  And frisk'd and browsed and bray'd,
  And many a clean spot made.
  Arm'd men came on them as he fed:
  "Let's fly!" in haste the Old Man said.
  "And wherefo............