[masraum]

Mice in the house sucks, but they are small and any hole big enough for their skull to fit through is enough for them to fit through. I think that means that a hole the size of a dime is big enough. It doesn't take much. If there was one, then I'd assume that there could be more, and I'd set another trap or two, probably around the perimeter of the room where you saw the first one. Leave them setup for a week and check them in the mornings. If you're lucky, you caught the scout. If not, then you may catch another 1-3.

I've had mice in a house that I was in a few times over the past 50 years. Usually a few caught via traps does the trick.