Raised hackles indicate arousal, either because a dog is frightened or is challenging another dog. Smooth hackles show a dog is calm.
Yawning may indicate anticipation or stress. It increases heart rate and blood flow to the brain. Filling the lungs with oxygen and removing carbon dioxide. In fact, it helps a dog energize his body and gathers his wits.
A relaxed tail means that a dog is calm and at peace. A tail head straight out, wagging rhythmically and slowly, means that a dog is cautious or on guard. Tail down indicates worry or uncertainty.
Licking the lips is a sign that a dog is worried or is trying to appease a person or another dog. A relaxed mouth means a dog is calm. Lips pulled back is a challenging or warning sign, especially when combined with a snarl.
Pawing is an appeasing gesture. Licking another dog's face is an invitation to play or sign of deference.