Confrontations can be tricky things. Here you have a cat that probably weighs 7 or 8 pounds battling a mouse that might weigh a single pound, if that. But these facts do not measure the amount of crazy in each. Not only does the little mouse act a bit deranged, he has some serious hops making the cat question any athletic superiority.
They have always said, "It's not the size of the dog in the fight but the size of the fight in the dog," or in this case, in the mouse. This mouse has plenty of fight.