The "zucchetto switcheroo" is a long-held tradition for popes and pilgrims.
A guest presents the pope with a brand-new white skullcap, and the pope is expected to take it and swap it with the one he's wearing on his head.
While many pilgrims are familiar with the practice, a newly elected pope usually needs a quick explanation from an aide or security guard when someone suddenly presents him with a fresh new cap purchased from the papal tailors at the Rome-based Gammarelli shop.
But once they know the drill, everyone from Blessed John Paul II to Popes Benedict and Francis happily has engaged in the tradition, letting the lucky pilgrim get a souvenir of a lifetime.
One lucky pilgrim at the general audience Wednesday in St. Peter's Square was a junior from Providence College, R.I., who is spending a semester studying in Rome.
When Pope Francis went through the crowds in his open popemobile, Joseph Day, a native of Rehoboth, Mass., stretched his arm out over the heads of his classmates to give the pope a zucchetto with a hot pink sticky note stuck inside.
According to news reports, Day had written on the note: "Providence College loves Pope Francis."
The pope took off his own cap and put on Day's gift, but then he gave it back after glancing at the note.
While sometimes Pope Francis does trade in his old skullcap, more often than not he has been choosing to keep his own zucchetto after he places the gifted one briefly on his head and returns it to the giver.