When we walk a reactive dog and he reacts, trying to explain that he's actually scared often falls on deaf ears aside stern faces. Fear has a varied appearance though, and exactly how it manifests in their behaviour, depends on the dog.
Hiding within herself is the default response of a dog with learned helplessness, or simply a dog who feels like they can't help themselves in this moment. Scientifically known as freeze she will tuck her rear under, avert her face and hope for the best. This response is characterised by stiffness, avoidance yet an inner belief that they can’t get away. Wide tongue, slow lip licking is often shown as an involuntary action.
Trying to run away is the flight response in action. Characterised by low body language, and speedy retreat, taking flight is a natural way that a dog will respond to danger if she has the choice.
Dogs won’t often choose to fight, because it contradicts survival. Wild wolves usually sort out their minor and even some major differences via negotiation because to fight means they get hurt which will naturally weaken the entire pack. Dogs too will not fight if they can help it as it's bad for self-preservation. We do however inadvertently encourage the fight reaction in them by exposing them to scary things without giving them the chance to escape.
For example, we have them on a lead and make them stay close to the thing they fear. When this happens to a dog they lose their option for natural flight and in its place they try to chase the scary thing away. This is the dog’s natural fight response and why we see them barking and lunging so often. It’s a behaviour that shouts, “don’t come by me I’m dangerous” but actually means “I’m scared and must look scary too”.