Today is Mortens Aften in DK, and according to the Danish tradition you should celebrate it by eating duck. Morten is the Danish name for St.Martin. Why duck? According to legend, Martin was reluctant to become bishop, which is why he hid in a stable filled with geese. The noise made by the geese betrayed his location to the people who were looking for him.
A stable filled with geese doesn’t seem the best choice if you wish silence… So people would eat goose to…celebrate? vindicate? I guess to get revenge. And then the duck became an easier, maybe cheaper, substitute for the goose.