A part of the celebration of Christmas in medieval French churches when parody of sacred services and social inversion were allowed and when clergymen were given license for light-hearted behaviour that was unthinkable during the rest of the year.
The Feast of the Ass, usually held on January 14, celebrated the role played in the Nativity by the humble donkey, the beast who carried Mary to Bethlehem, who stood over the baby Jesus in the stable and who carried the Holy Family to safety in Egypt when King Herod was bent on killing the infant. As the clergy or students paraded toward the church where the ass was to be honoured they sang a “hymn of praise”:
From Oriental country came/ A lordly ass of highest fame,/ So beautiful, so strong and trim,/ No burden was too great for him./ Hail, Sir Donkey, hail!
For the ceremony itself a donkey was often brought into the church and during the Mass which ended the service the congregation made donkey noises. Like the Feast of Fools, with which the Feast of the Ass was linked, this sort of behaviour eventually grew too outrageous to be tolerated and the church moved to suppress it. By the sixteenth century it had almost entirely disappeared from the Christmas scene.
No wish to be sacrilegious, but I would be charmed if my church tried that one year!