Direct eye contact means that a dog is feeling bold and confident. Casual eye contact means he's contented. An averted gaze means indifference. Dilated pupils indicate fear.
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.
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.
Tail held up and wagging fast indicates excitement. An erect tail is a sign of alertness. A tail held between the legs is a sign of fear.
Pawing is an appeasing gesture. Licking another dog's face is an invitation to play or sign of deference.