In the course of moving a light, I had to enter this 24x24x4 pull box. The box was properly closed, with no open KO's. Nor were any wires damaged. Yet, in the bottom, near the 2" conduits, we found two mouse skeletons.
The place is 17 yrs. old; I can only guess they have been there that long.

I know what you mean. I still can't figure out how things like mice and snakes manage to get into fully-closed enclosures. I found mouse remains in an outdoor trough at a gas station where every single conduit entering it was only 3/4" and was sealed.