I got a bit verbose here, so my apologies.
Anyway, about a week ago I noticed this N.lowii had a damaged lid. I thought maybe I had broken it while watering or moving plants around. (All photos were taken today.)
Yesterday I noticed similar damage on a young Nepenthes ephippiata up on a shelf, so I then took a look at a larger plant and found this:
I suspected a critter was at work, so last night I set a trap near the larger N. ephippiata and caught a mouse.
After taking the above photos and disposing of the mouse, I peeked in the pitcher. At least the plant received some food in exchange for the lid damage!
Guess this qualifies as a "mouse toilet".
(Mice seldom act alone, so I'll be setting more traps...)