Before I installed my engine in the car for the first time, it was sitting with no plugs. I happened to look through one of the spark plug holes and saw that I had mouse poison pellets on top of the piston.
When I had a somewhat rusty Beetle, a mouse got stuck halfway through a hole in the kick panel.
I have an ultrasonic mouse repeller in the garage. I don't if it really works but I haven't noticed evidence of mice in the garage. I do find mouse turds in the garage attic.