The mouse is Om Nom's companion introduced in Cheese Box, and the gameplay of the box revolves around it. Each of the levels in Cheese Box has two to five holes; the mouse visits them in turns, not controlled by the player. If a candy passes by, the mouse will grab it and carry to other holes. The mouse releases the candy on a tap.
Unlike real-life mice, the mouse shows no interest in candy and gives it to Om Nom willingly.
Much like lanterns, the mouse makes it easy to move the candy across the screen.