Neutral Mood

• Before a dog's aggressive posture can be recognized, the owner must know how his dog looks when in a neutral mood. According to the American Society for the Prevention of Cruelty to Animals, when a dog is calm and relaxed, she will typically hold her head and ears up. The dog's mouth will be open, not tense. A relaxed dog balances her weight evenly between all four paws. A neutral mood is demonstrated by a relaxed, possibly wagging, tail.
  
  

Pre-Aggression

• Dogs take a certain posture when they become alert and begin assessing their surroundings. The Humane Society of Silicon Valley says this state may only last a few seconds before becoming aggression. When a dog's tail is straight and stiff, the mouth is closed and ears are pushed forward, the owner may distract the dog, stopping aggression.
  
  

Aggressive Head Posture

• Dog aggression is signified by a head held high, a wrinkled nose, and a mouth that is open and may be snarling or growling. The dog's lips may be curled back. Herding dogs, such as Welsh Corgis, Border Collies and Australian Shepherds, may show aggression by nipping at a child's heels as she runs and plays. In this way, the dog uses his mouth to show dominance over the child. The dog's ears are pinned back, firmly against the head.
  
  

Tail Posture

• When dogs act aggressively due to fear, they often put their tails between their legs. Being pack animals, dogs will sometimes try to take over the alpha role. This type of dominance aggression is seen when dogs hold their tails high and stiff. 4H Pet Pals says dogs may also wag their tails with short, quick movements.
  
  

Aggressive Eyes

• During defensive aggression, dogs' pupils may dilate. An attack may be near when a dog's eyes are narrowed and fixed on a subject. A prolonged stare signifies a challenge. A dog demonstrating fear aggression may look away for brief periods of time.
  
  

Torso and Legs

• Aggressive dog posture includes the placement of all four paws firmly on the ground. In order to appear larger, an aggressive dog may lean slightly forward. When preparing to lunge, the dog slightly bends all four legs and lowers his shoulders. The hair on the dog's back, the hackles, often stands straight up.