Supposedly, since that time, any candidate for the pope undergoes an intimate examination to ensure he is not a woman (or eunuch) in disguise. This involved sitting on a chair which has a hole in the seat. Someone then looks under the chair to ensure the new Pope is male.
The Vatican deny the existance of the chair (supposed held in an anti-chamber there), and also the existance of Pope Joan.
There is little evidence that Pope Joan ever existed.