On Mount Cyllene a wanderer named Tiresias came upon two snakes coiled together and struck at them — and his own body answered. The record says that, having "wounded them", he "was turned from a man into a woman"; and only long after, "on observing the same snakes copulating again", did he change back. The fullest witness to this doubled crossing of sex is the Greek one: Apollodorus's The Library (a Greek mythography compiled in the 1st–2nd century CE), read in the translation of Sir James George Frazer (1854–1941), the Scottish classicist who furnished the text with its notes.

Because Tiresias had lived on both sides of the body, Zeus and Hera called him to settle a quarrel no one else could judge — who takes the greater pleasure in love, the man or the woman. He weighted it heavily toward the woman: "if the pleasures of love be reckoned at ten, men enjoy one and women nine", or, in the verse the record also keeps, "Of ten parts a man enjoys one only". The reply cost him his eyes — Hera blinded him for it — but "Zeus bestowed on him the art of soothsaying", so that the price of the answer was also the making of the seer.

Frazer's note beside the passage remembers a variant the compiler did not tell: that it was "killing the female snake" that first made Tiresias a woman, and killing the male that "changed back into a man." Only the Greek witness is wired to served text here; the Irish, Hindu, and other traditions filed under this change wait unread, though this one carries the shape whole. If the one mortal ever trusted to weigh the pleasures of both sexes had to be struck blind for saying what he found — what was it the gods did not want spoken aloud?