Depending on the breed of mouse starkers, they can flatten themselves so that their entire body is no taller than the height of their head, and then scoot under doors or through holes you could not possibly imagine them getting through.
That's the thing, there are no entry points like that into the main house. The entry/exit doors are sliding except one, and it has only 1.5cm gap between it and the floor. There is the garage, and it's possible they might be able to squeeze under the tilt doors, but there is still no visible access to the man cave [downstairs area] or main house upstairs. My niece even had a pest control expert out and even he could not find where they were getting in.... but, as I type this, I think I may have discovered the method of access.
Yeah, so what happens is this! The mouse/mice are scurrying around outside when a bird or birds grab it/them and soar upwards and drop them/it on the roof - which may be merely be accidental or a conspiracy between them, I'm not sure - where upon the mouse/mice get under the roof, into the wall cavities and into... er, no, that doesn't work, either... no access from within the wall cavities.
Oh well, the thread is entitled "Weirdos".