Okay, so I'm really feeling this idea so tried to get down a bit more detail! 
I'm a little unsure how to go about tackling the premise. I think maybe it would be something based around 'role-reversal'? Along the lines of, Life takes a turn when everything is reversed/backwards or Humans must be stopped from escaping the zoo, so the pest controller is called.... to refer to the odd world it's set in where rats are human-sized and humans are rat-sized... I feel like I'm getting somewhere, kinda.