At Rimini in 1227, St. Anthony of Padua was preaching against the Cathar heretics. A wealthy heretic named Bonvillo challenged him: if Anthony could prove the Real Presence, Bonvillo would convert. Bonvillo proposed that his own mule be locked up for three days without food, and then brought into the public square between a measure of fresh oats and a monstrance containing the Blessed Sacrament.
Three days later, before a great crowd, the starving mule was led into the square. It passed the oats without a glance, walked to the monstrance, and knelt on its forelegs before the Blessed Sacrament. Bonvillo and many of his household converted that day. The episode is recorded in the earliest Vita of St. Anthony.