Just put your cursor near the mouse to scare it away from your cursor into the cheesy puffs. simple, right? Oh also avoid red objects because they make the rat "sleepy" when they touch it.
s + 2 to activate stage 2 and s + 3 to activate stage 3 and so on, its a bit weird though because its a temporary Dev feature, for example you have to go s2 s3 then s4 to functionally get to stage 4 or else it breaks.