A dog usually wags its tail(摇尾巴) to show that it's friendly. The dog is saying, "I feel happy!" by wagging its tail.
This dog is having fun. How do you know that? The dog's tail is in the air. Its ears are up. It looks like it is smiling.
This dog is frightened. How do you know that? It is hiding(躲藏). It is saying, "I feel afraid." Some dogs use other ways to show this kind of feeling. They may make their ears down. They may bark(叫). These dogs are also saying, "I feel afraid."
This dog is angry. How do you know that? It is making a deep(深的) sound. It is showing its teeth. And it may bite(咬) you, so never play with an angry dog.
Now you know how to watch and listen to a dog. You can look at dogs' ears and tails.You can look at how dogs stand. You can listen to the sounds dogs make. Now you can understand how dogs "talk"!