"Are you a cat?"
(I wrote it about statements, but the same applies to questions, only the intonation is different and in writing there is a question mark at the end ;-))
When speaking about first (I, we) or second (you) person, one uses verb to be (być) with instrumental to connect subject and predicate. So (ja) jestem psem (I am a dog), (ty) jesteś człowiekiem (thou art a man), (my) jesteśmy fantastami (we are sci-fi fans), (wy) jesteście graczami (you are gamers).
When speaking about third person (somebody or something else), then it is popular to connect subject and predicate by neuter pronoun to: ona to pies or ona jest psem (she is a dog), krzesła to meble or krzesła są meblami (chairs are furnitures) etc.
Clauses like ty to kot are perfectly understandable, but they sound very unnatural.
We just consider using the 'to' construction after a personal pronoun to be very, very clumsy.
Let's take a more probable sentence: You are a man. I googled "ty jesteś mężczyzną" and got 23 000 results. Then I checked "ty to mężczyzna" and although at first it gave quite a big number of results, going to the 2nd page actually shows that the number of results is... 11. And a few of them aren't even exactly what I was trying to search for.