Count Mouse Droppings

I read in the paper today that a restaurant was closed because the city of Chicago found over three hundred mouse droppings in the establishment. That must be a great job, to count mouse droppings. Poor schmuck probably can't use the restroom without thinking about work. A few things come to mind:

Why do they have to count the number of droppings?
What is the cut-off for droppings? Is one hundred okay? Fifty?
Did anyone actually see a mouse? Perhaps rats are bringing the droppings into the place to frame mice, in which case the place shouldn't be closed.

What happens if they find 1000 or more mouse droppings?

Are the mouse droppings in any shapes? For example, is the a dropping in the shape of Mary? That's what we really want to know.