Thanks for the post and your timing is perfect. I have been dealing with a mouse issue most of the winter. I set several glue traps out but didn't manage to catch a thing in months. I set some snap trap out and caught one of the little turds the next day. Your picture reminded me I need to be more vigilant and check to see where that have been and not assume they haven't done any damage.
I worked briefly for a pest control company and the owner would laugh at homeowners that used the foam in a can. Mice can easily gnaw thru wood so I have little faith in the foam...it just isn't dense enough to keep them out. We used copper mesh (similar to steel wool but copper doesn't rust) and mortar caulking to fill entry holes where mice were getting in...apparently mice (and rats) do not like the texture of the mortar caulking and can't gnaw thru metal screen or mesh.