Pope Joan?

"According to medieval legend, Pope Joan was a female pope who reigned from 855 to 858."

"Supposedly, since her 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. The most junior deacon present then feels under the chair to ensure the new Pope is male: 'And in order to demonstrate his worthiness, his testicles are felt by the junior present as testimony of his male sex.
When this is found to be so, the person who feels them shouts out in a loud voice testiculos habet ("He has testicles") And all the clerics reply Deo Gratias ("Thanks be to God"). Then they proceed joyfully to the consecration of the pope-elect"

It all makes sense now.