Dogs are canids and humans are primates.
We do not have a common language to communicate with each other. Most of us have lost the ability to communicate with our dogs telepathically since childhood. This leaves body language as the only way they have of communicating with us. I often give demonstrations on the use of service dogs for PAWS With A Cause, where I work as a field instructor and presenter. Timmy was always falling in the well or something, and Lassie was forever having to go get someone to help.