Has anyone ever called you an animal and you didn’t understand why? Maybe they were just using an idiom.
Animal idioms are funny because they don’t always make a lot of sense. However they are a very important aspect of the English language because you can’t get away from them. They are used all over pop culture in movies, TV shows and especially music. When you watch sports you might cheer for the dark horse. When you read about historic people, you may discover that they were lone wolves. People in the news are often treated like guinea pigs. If understanding these expressions gives you butterflies in your stomach, you should probably study them.