I'm not quite sure what sort of mental model one must have to pose such a question (maybe some sort of reincarnation-like spirituality where all animals and humans have the same soul/spirit substance that after birth has to figure out what kind of animal it was slotted into this time?).
How does a rock know to be a rock? Why doesn't it get confused and become water?
A cat doesn't need to know that it "is a cat". It just has a cat brain and a cat body, so it does cat stuff.
Of course, there is some learned behavior, parental socialization and some "culture"-like practices is certain species, but it's not like cats may forget "how to cat". Do you think a fish may get confused and suddenly forget to be a fish and instead act like a mouse?
How does a rock know to be a rock? Why doesn't it get confused and become water?
A cat doesn't need to know that it "is a cat". It just has a cat brain and a cat body, so it does cat stuff.
Of course, there is some learned behavior, parental socialization and some "culture"-like practices is certain species, but it's not like cats may forget "how to cat". Do you think a fish may get confused and suddenly forget to be a fish and instead act like a mouse?