She had a swim and a run around and then her favorite activity, chasing a ball. As we played, a group of other dogs came past and, as usual, Penny didn't want to interact with them while she had a precious ball to guard. One friendly golden retriever was determined to keep sniffing Penny's rear end and she seemed to be quite irritated but the other dog either wasn't picking up on the body language or didn't care. Eventually Penny snarled at him, but of course that's a tricky thing to do when you have a ball in your mouth!
I wasn't sure whether the sniffing was in fact a friendly gesture, so I was interested to come across a site on the Net that has detailed descriptions of dog body language accompanied by sketches and photos.
Two interesting items were:
Some confident, dominant dogs will roll on their backs, exposing their bellies, in an attempt to reassure a more shy or submissive dog, or to get that other dog to play. They will be relaxed when they do that, and usually still look the other dog in the eye. Sometimes mounting ("humping") another dog is a sign of dominance, but not always; this often-misunderstood gesture can also be used by a lower-ranking dog to try to demonstrate his allegiance with a higher-ranking animal.
Note that among dogs, the hierarchies are usually maintained and demonstrated very casually and almost always by more submissive members of the pack. Very high-ranking animals very seldom demonstrate their rank, unless they lack confidence. Most demonstrations and almost all fights that occur over rank are done by the middle-ranking or unconfident members.
The article was by Stacy Braslau-Schneck and ended with a list of lots of links with more information.One was a body-language quiz. I managed to get most questions right, but not all.