Aggression in a dog is not uncommon; however, it could be problematic if there are other underlying causes. Some breeds are more aggressive than others. These include Spaniels, Terriers, Lhasa Apsos, and Rottweilers, and others, but aggression can appear in any breed. Medical conditions and the after-effects of medical procedures can also cause an animal to exhibit aggression even towards familiar people. Aggression is accompanied by a terrifying body posture and facial expressions. Mostly this is seen when the dog feels cornered or is provoked. Primarily, aggression could be categorized into offensive and defensive. Sub categories could include inter-dog, dominant, defensive, possessive, territorial, predatory, parental and those induced by fear, pain, or punishment.
Some signs normally seen in offensive aggression are
Frozen stance
Growling
Snarling
Snapping
Head up
Tail up
Direct stare
Immobile face
On the other hand, signs of defensive aggression include:
Head lowered
Tail down
Body withdrawn