Just as dreams are partly determined by day residue, fantasies are triggered by various stimuli. Three common fantasies are examined and referred to anatomic and physiologic determinants. The stone as it appears in fantasy formations has qualities shared by the penis; the taboo against looking at a god may have had its origin in the retinal damage suffered by sun worshippers; the fantasy of ear impregnation may be influenced physiologically by the connections between the ear and the abdominal viscera.