Symptoms can vary
Typically after a warm-up of about ten minutes:
Rigorous shaking of the nose
Vertical flicking of the nose
Rubbing of the nose on the ground, legs, or objects
Jerking head movements
Pullin on the rein
Disorientation that can lead to falls
Despite extensive research no single cause has been identified in relation to headshaking. This makes it important to rule out mechanical irritants such as awns that can stick inside the nostrils or dental issues.
Sensitivity to insects is another reason. The Nose Net provides relief for this as well since horses quickly realize that they are protected and insects are unable to get into the nostrils.