Christine's shotgun shells have all been fired; that is, the firing pins are all indented, meaning they have been shot.
At the end, the bulldog Boozer is trying to attack Clorissa, the close up shows a black bear toy.
Christine says she's out of ammo, but she has lots of shells left in her Bandolero ammo belt.
Clarissa and Biff block the door that opens outward by pushing objects against it. Fruitless enterprise.