There have been some strange rustling noises underneath the house. Last year when this happened, it was due to a resident stinky skunk. After waiting one evening past midnight for the skunk to exit, Dr Hyde had carefully blocked up all the entrances to the crawl space with loose bricks, so we were surprised that anything could have gotten back in. But sure enough, some of the bricks in one location were displaced.
Dr H wanted to brick up this entrance again, but I pointed out that if there was another skunk under the house, and it was trapped and died, I would be wrathful in the extreme. How to make sure the beast was gone?
Dr Hyde's solution: he took the baby sound/video monitor, which we usually use to make sure the cat has not smothered the baby, and planted the camera portion outside over the crawl space entrance, running the power cord in through a window. Then he stayed up late with a fussy Small, watching the video monitor.
A little after midnight, an animal exited--a sleek possum. Dr H waited to make sure there were no more possums, then re-bricked up the crawl space.
Today, the camera is still outside, and I am relying on ESP to make sure the cat hasn't leapt into the bassinet.