I went so far as to take a flashlight around looking at all the ceilings and walls, trying to find water damage. I even went up into the attic and sat quietly, trying to hear a drip.
But I think I have discovered his secret tonight.
I went into the guest bathroom and I noticed that the sink was drip, drip, dripping. A significant leak that I must get fixed sooner rather than later as there is no telling how much water I've already wasted.
I also just happened to notice that the entire bowl of the sink is plastered, absolutely plastered with little gray hairs.
What kind of cat, I ask, lies in a dripping sink!?
My kind, apparently.
At least I no longer have to worry the ceiling is about to cave in...