So the "thing under the house" that Mom told me about.... I found it. I heard it this morning, outside the kitchen window where she said she thought it was coming from the ventilation grate under the house, under the window where Olin was sitting staring intently downward. I went outside to confront whatever beast was clawing away down there, but saw only an empty feed bag that Mom had propped against the side of the house under the window, yesterday evening, shortly before she heard the monster under the house.
Scritch scritch scritch! Ah, the monster is clearly IN the feed bag. I laughed. The monster had two beady black eyes, a little twitching nose, lots of whiskers, and was about 5 inches long from nose to tail. ;-)
The monster has, uh, "gone to a better place" shall we say. I'm sure the world will sleep better tonight.