 It was believed that the "Aos Sí" needed to be propitiated to ensure that the people and their livestock survived the winter.From at least the 16th century, the festival included mumming and guising, which involved people going house-to-house in costume (or in disguise), usually reciting verses or songs in exchange for food.It may have originally been a tradition whereby people impersonated the "Aos Sí", or the souls of the dead, and received offerings on their behalf.