Teiresias was a wise, blind seer with the most extraordinary experience of having lived part of his life as a woman (some say the latter was the cause of both his blindness and prophetic gift, since he was called to settle a dispute between Zeus and Hera, who argued whether the man or the woman enjoyed the sexual act the most. Teiresias agreed with Zeus and said it was the woman. Hera got furious and deprived Teiresias of his sight. Zeus then gave him the gift of prophecy as a compensation).
In "Menippus - A necromantic experiment" it's Teiresias Menippus wishes to speak with during his visit in the Underworld (probably as a hint to the Odyssey where Odysseus too seeks the advice of the dead seer). Was it the spirit of Teiresias that came to Theo and Melito? Probably. When was the last time you heard a seer give a straight answer? ;)