Mice don’t always come in multiples. Sometimes a mouse gets in a building just simply seeking warmth, and then food left out will attract that mouse to your room. If you want to test whether you have more mice, leave some sticky traps out overnight – put a couple of them (or more) together with a little bit of peanut butter (mice can not resist) on the edge and place them in a way that the mouse would have to travel onto the sticky part to get at it. If you don’t have a mouse by the next morning, then you no longer have a mouse problem.