The Mass of Saint Gregory the Great, attributed to Diego de la Cruz; Philadelphia Museum of Art, Pennsylvania, USA; c.1490
I have posted numerous versions of this episode before. In the earliest versions of the story, a woman was heard to laugh while the Pope was saying Mass, exclaiming that she could not possibly believe the bread to be God since she herself baked it. The Pontiff prayed for a sign, and the Host became a bleeding finger.
Later re-tellings record the doubter as one of the deacons, and by the time the Middle Ages had come, the bleeding finger had been transformed into the Man of Sorrows.