Why do dogs have their tails between their legs?

The dog's tail does not refer to the tail itself, but to the bottom of the tail. When the tail hangs down and is tightly sandwiched between the hind legs, the timid dog will effectively block the odor signal from its anal area.

Dogs living in the wild have a strict hierarchical relationship, and clamping their tails has become an important signal and humility of the weak in front of the strong. Therefore, seeing a dog with its tail between its legs in life can be understood as becoming timid and fearful when encountering an enemy, and wanting to run away. The primary function of a dog with its tail between its legs is undoubtedly to control the sense of smell, but as a secondary visual signal, it can not be ignored.

Extended data:

Pinching the tail is a way for dogs to protect themselves, which can protect the weak members of the group from the attacks of high-ranking members. But there is a difference between a dog and a wolf. All wolves have a special anterior caudal gland on their tails, but dogs don't.

There is another key point in the dog's tail-lifting and tail-dropping movements. Any animal that observes the meeting of two wolves or dogs from a distance can know which one is in the dominant position and which one is in the inferior position by looking at the silhouette of their limbs.