Young Frankenstein Episode 5: Corpse tug-o-war

We finally get through the remaining credits and push into the sitting room of the Castle of Baron von Frankenstein where a coffin is setup in front of a roaring fireplace. The coffin is ripped open to reveal a corpse holding a box. A set of hands moves into the shot, trying to pull the box away from the fingers of the corpse, only to be denied by a supernatural death grip on the box. What's inside? Why is someone stealing it? And, who keeps a coffin inside their family room??