Another reason this one deserves to be revived. From Archdale King's page-turner, Liturgies of the Primatial Sees
, p. 44, which has nothing to do with pre-Cambrian fish:
A serious mistake in either the chant or the ceremonial entailed a penance known as a priva, and the culprit had to go behind the altar where he finished the Office in a lower voice. If, however, the error occurred during Mass, the celebrant was compelled to sing the preface, Pater noster, embolism, etc., in a doleful voice.
You can just imagine the reactions from the pews. "Oh dang, it's Fr. du Pont again...let's see if he can get through the Introibo
at least without screwing up...ah, here we go, here comes the moaning. Looks like you owe me ten francs, Thierry, pay up."