There are big and small mammals. A mouse is a mammal.

Fast Fact: Mammals breathe air.

A cat is a mammal. It is bigger than a mouse.

Fast Fact: Mammals have hair.

A dog is a mammal. It is bigger than a cat.

A lion is a mammal. It is bigger than a dog.

A polar bear is a mammal. It is bigger than a lion.

Fast Fact: Mammals care for their babies.

An elephant is a mammal. It is bigger than a polar bear.

A whale is a mammal. It is bigger than all the mammals in the box put together. Wow!