Mummering is when people dress up in silly costumes and go around to their friends' houses during the Christmas season while wearing a mask or veil over their face. They knock on the door and when the person answers, they try to guess who the mummer is by listening to their voice and the way they act. If the person can't figure out who the mummer is, they usually offer the mummer a treat or a drink, and then the mummer moves on to the next house. It's a fun and festive way to celebrate the holidays with friends and neighbors.