Many have read Oedipus rex, only to confused by the vague reference to a riddle. Well, it is a very simple and common riddle now, but I suppose it was very cryptic to the people of Thebes. The sphinx sat outside the gates of Thebes and asked the question of each person who entered. If they answered incorrectly, then they sphinx killed the person. If they answered correctly, then the sphinx would destroy herself.
Question:What goes on four legs in the morning, on two legs at noon, and on three legs in the evening?
Answer: A man, who crawls on all fours as a baby, walks on two legs as an adult, and walks with a cane in old age.
Metaphors such as morning, noon and night are commonly used in riddles such as these.