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 existence of the chair (supposed held in an antechamber there), and also the existence of Pope Joan.
There is little evidence that Pope Joan ever existed.