If there's one thing that the classic cartoon Tom & Jerry taught me as a child is that cats and mice really don't get along. And sometimes mice hit cats with hammers. And lure them into backyards with lurking bulldogs. And gravity is optional.
In all seriousness though, cats are supposed to love killing small animals like birds and mice, because life isn't a Disney movie and they're genetically programmed to be carnivorous killing machines.
So if you've got a cat in your house and all of a sudden you find a rat that you're not all that stoked about getting rid of yourself, then you'll probably put your cat in said room with that rat and expect the cat to go to town on the rodent, right? Well, that's what this kid thought would happen.