Have you read or seen any Giradoux? In "Penric's Fox", the passage on whether ghosts can lie reminded me of "The Enchanted", in which the heroine, has a suitor who is a ghost. She remarks that he can answer the riddle of Death. Her living suitor responds: "What makes you think the dead would know the answer? If the dead know any more about death than the living know about life, I congratulate them on their insight!"