If it looks, like a duck, walkes like a duck and even quacks like a duck, it's not necessarily a duck.

If it looks like a duck, walks like a duck and even quacks like a duck,
It is not impossible that it might be a duck.

If it looks like a duck, and quacks like a duck, we have at least to consider the possibility that we have a small aquatic bird of the family 'anatidae' on our hands.