When Bart approaches Santa's Little Helper's doghouse with food, something inside viciously grabs the food and he is puzzled to see the dog sitting next to him. When he looks inside he sees that a vicious badger has taken up residence.
Along with Homer, they make several failed attempts at drawing the creature out before Homer calls animal control. Unfortunately, he was unable to call for animal control due to a change in the area codes. The badger presumably led an army of badgers to attack Springfield in the ending.