How can you tell a mammal is a mammal?

at the time of birth mammals produce milk and they are warm blooded animals

mammals have faur or hair like were a mammals

If they reproduce

You very well can tell a cat is a mammal, as the cat feeds milk to the kittens. Plus it has fur, warm blood, and certainly doesn't lay eggs.

They're warmblooded animals that breathe air. They have a tiny bit of hair. Some have hair throughout their lives, and some only have it when they're tiny babies.