Marmaduke has taught his owner-boy the two most important principles by which he leads his life: get into mischief (in this case with dozens of snowballs) and make Owner-Lady's life revolve around yours via selfishness (such as taking up all the room her refrigerator with snowballs) and ignorant destructiveness (such as choosing to fill the refrigerator rather than the freezer with said snowballs, which will eventually melt and cause, at best, an awful mess).