Aren't you glad humans don't have tails, so that human body language cannot work in the same way as dog body language?
" "Dogs are much better at reading each other's body language than we are," says Dr. Bell. "Dogs that are behaving appropriately in social systems use their bodies and tails to communicate with other dogs even as they are observing the tails and body position of other dogs. This helps them avoid unnecessary conflicts."
Dogs also wag their tails to spread their natural scent from their anal glands. Each dog has a scent that's unique to him or her. An "alpha" or dominant dog that carries his tail high will release more of his scent than a dog that carries his tail lower. Often, when we see a dog holding his tail between his legs, he's frightened and doesn't want to release his scent. This is his way of flying under the radar."