When bringing my dog to the groomers tonight, he yawned the entire ride there. I wasn’t sure what could be causing it? Tiredness? Stress? Excitement?
The general consensus is that nobody knows. Several blogs I skimmed tonight suggest that it could be for all three reasons above. Based on his demeanor, I would guess excitement in this case. I’m going to try another groomer next time to see if his actions are different and maybe help pinpoint his temperament about hair cuts.
This post from the blog of Bark & Clark details the physical signs of each yawn and what they could mean in human words.
http://barkandclark.blogspot.com/2011/10/why-do-dogs-yawn.html
Dexter's Dog Days 