Fearful aggression occurs when a dog (or for that matter any mammal) reacts to feeling threatened by growling, snarling and/or barking. At the point of fearful aggression a dog is already feeling vulnerable probably from a past memory of being hurt or injured by something else. The fearful aggression is used as a way to scare away whatever is perceived to now be threatening.
Humans also possess and act with fearful aggression when they feel threatened or in danger. The unconscious experience which many people will validate is that given that they already feel vulnerable from some prior trauma they believe they will not survive a second and now impending one.
One of the places you can observe fearful aggression in full display is in many of the politicians who are running for office during this election especially as they are feeling more desperate.
There is a nifty way to see fearful aggression for yourself. In the following pictures, take an index card or business card and block out the person’s mouth and look at their eyes and then block out their eyes and look at their mouth.