Rats/mice are everywhere. Occasionally, they will be moving in and out through the air bricks and under the floorboards, usually not causing any harm. In your case, cute ratty visitors are inevitable. There are far more of them in the world than most people would think.
Had a visit from a rat recently, and it was hiding behind the kitchen plinth, always making a bloody noise during the night. Removed the plinth and found out that it had gnawed through the adjoining kitchen cabinet. Cleared the area, left the area open and waited for it to return. However, sadly, I've no idea where the rat escaped to because I haven't seen it ever since. Rats look for places which are dirty and have food available for them to eat.
About a year ago, it chewed through the toilet flexi pipe. So I had to replace it with a solid soil pipe.
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