You cannot do what you want. The way polymorphism works is by doing what you are seeing.
Basically a cat always knows it is a cat and will always behave like a cat regardless of if you treat is as a Cat, Felis, Felinae, Felidae, Feliformia, Carnivora, Theria, Mammalia, Vertebrata, Chordata, Eumetazoa, Animalia, Animal, Object, or anything else 🙂