When assessing dogs, I often look at the mouth. With such a strong interest in canine aggression, I have spent a lot of time looking at this part of dogs’ bodies, and wrote about my observations  recently in my local newspaper.
The basics of interpreting the internal state of a dog from the mouth involve the following questions: Is the mouth open or closed? Is the dog panting? Does the dog display an offensive pucker, a fear grimace or a tooth display?
The answers can enlighten you about whether a dog is happy and relaxed at the moment, rather than feeling anxious or perhaps fearful. The mouth provides clues about the amount of confidence a dog is feeling as well as the likelihood of going on the offense and behaving in an aggressive way.