While our unwanted houseguests aren't known for their subtlety, they can be surprisingly discreet at first. The most common signs of mice include small, dark droppings (about the size of a grain of rice), scratching sounds in walls or ceilings (particularly at night), signs of gnawing on food packaging or wooden surfaces, and distinctive musky odours. You might also notice greasy marks along walls and floorboards – mice tend to follow the same paths, leaving behind evidence of their regular commute. If you've spotted any of these signs, it's best to act quickly, as mice are prolific breeders who consider an unaddressed invitation as permission to extend their stay indefinitely.