Why they call it a "mouse hole"

[Berdan]

I removed the panel below the bathroom sink to access the shore power cable area and found a mess in there. Looks like this was the impetus for the previous owners to foam up all the openings in the belly of the trailer and foam/steel wool the water pass through up to the bathroom sink. I don't think they actually discovered where their mouse was living or how it was getting in but all indications is it was coming through the shore power mouse hole. Also the adjacent area under the shower was spotless it did not wander there.
Anyway the area cleaned up nicely with some bleach water and a lot of scrubbing.

I am wondering where the mouse procured the fiberglass insulation from though.