He was asked to be sent away because he knew too much. Then he came back and everyone the truth about Oedipus. It was a very dramatic moment.
Teiresias is a blind prophet, led by a small boy. He/she knows the truth about Oedipus's parents. Oedipus calls on him to find Laius's killer but claims that Oedipus is the killer. However, the oracle believes Teiresias is telling the truth. He is part male, part female.
Sometimes comically obtuse or fickle, sometimes perceptive, sometimes overdramatic, the Chorus reacts to the events onstage. The Chorus’s reactions can be lessons in how the audience should interpret what it is seeing. they can sway Oedipus and actually change his mind.