I'm broody

Occasionally a hen will have an instinctual urge to sit on and hatch eggs.  This behavior is called being "broody", and Buffy has been afflicted since the weekend.  She won't come out of the nesting box except to eat and drink a few times per day, and otherwise just sits in the box, hatching her chicks.  The weird part is, she isn't sitting on any eggs at all - broodiness overcomes the hen whether there are eggs or not.  If I approach her she puffs up her feathers and makes wookie noises.  She should snap out of it in several more days.