What I found out was that when a dog yawns that means that they are stressed.....I never knew that and I don't know many people that do. She does obedience and agility training. She has given me some really good pointers as to how to get Nala to go by people. It's not the dog that you are training it's yourself. You have to learn their "signals" as to when they have had enough. It was really good.
Yup, my understanding of it is that yawning is a "calming signal" for a dog, basically something that they do to try to calm themselves down when stressed. Other things that they might do are lick their lips or sniff the ground.
So, you can often use these signals right back at your dog to help encourage them to calm down. If your dog is in a stressful situation - let's say that Ranger is nervous about a dog walking by him, I can scatter some treats on the ground. As he sniffs around for the treats, not only is he getting a yummy snack which creates a positive association with the presence of the other dog, the actual act of sniffing is inherently calming to him. I can also help out by sending him signals such as turning my head to the side and yawning while he is watching me (showing that I am calming myself and there is nothing to be upset about) or licking my lips (same thing).
Dogs are also very clued into subtle things that we might not even notice like our breathing. If I am tensed up and stressed and breathing very shallowly and rapidly, Ranger will clue in on that and often act accordingly. If I take a few deep breaths and give him a smile and a yawn, I am sending a whole different message...
Isn't doggy communication fascinating? There are several good books about this stuff out there...