The mention of the crossroads (strictly a "place where three roads meet") reminds Oedipus of his past. He begins to worry, and worry more when Jocasta describes Laius ("his build was similar to yours"), and his escort of five men. He asks her to send for the surviving witness, who (significantly) had begged to be released from service when Oedipus became her husband. (He will turn out to be "The Old Shepherd"). Now he explains the reason for his fears, fears that he may have unwittingly been the killer of Laius, and thus the person whom he himself cursed.
Why had he left Corinth, and his parents Polybus and Merope?

• Because of a quarrel with his parents?
• Because of doubts that Polybus was his father?
• Because he killed a man who insulted him at a banquet?