Once, Tiresias happened to see the goddess Athena completely naked while she was bathing. Full of shame, Athena tried to cover his eyes with her hands and made Tiresias lose his sight.
Chariclo, the mother of Teiresias, was heartbroken. So she decided to go to Athena, who was a close friend of hers, and beg her to restore the sight of her son.
Unfortunately, Athena lacked the power to do so. However, she sent a snake to Tiresias to purify his ears instead. From that moment on, Tiresias was able to understand the language of the birds entirely.
Furthermore, Athena gave Tiresias a cornel-wood staff, enabling him to walk like a man who can see.