duck egg

from The Collaborative International Dictionary of English v.0.48

Goose egg \Goose egg\
   1. In games, a zero; a score or record of naught; -- so named
      in allusion to the egglike outline of the zero sign 0.
      Called also {duck egg}. [Slang]
      [Webster 1913 Suppl.]

   2. A bump on the skin caused by a blow, especially one on the
      head.
      [PJC]