Cats are the most popular pets among Americans. So it is not surprising that there are a lot of expressions about cats. Some cats like to catch small birds, like canaries  . If someone looks very proud and satisfied with himself, we say "he looks like the cat that ate the canary." Sometimes, a cat likes to play with a small animal it catches. So if you "play cat and mouse" with someone, it means that you change between different kinds of behavior when dealing with another person. For example, a girl might offer something sweet to her little brother and then take it away when he reaches for it. Americans might say that something is "the cat's miaow" or "the cat's pajamas " to describe something that is the best or finest. "A copycat" is someone who acts just like someone else or copies another person's work. "A fat cat" is a person with a lot of money. If you tell about something that is supposed to be a secret, we say you "let the cat out of the bag". If you are not able to speak or answer a question, someone might ask you if "the cat has got your tongue " Have you ever watched children in a classroom when their teacher leaves for a few minutes? "When the cat's away, the mice will play" means people sometimes act badly when there is no supervision  . You may have heard the expression "curiosity killed the cat". This means caring too much about things that are not your business might cause problems. If you have ever had cats as pets, you know it is difficult to train them or to get them to do something. Cats are not like Sheep or cows that can be moved in a group. So we say a difficult or impossible job is like "herding   cats " What can we learn from the passage?
The expression "a fat cat" is used to describe someone who is very fat. The expression "play cat and mouse" usually means "play tricks on others". It is more difficult to keep sheep or cows than cats. There are more expressions about cats than those about dogs.