Horses learn to predict what will happen next via classical conditioning.

Previously meaningless stimuli start to predict meaningful activities such as eating or being zapped by an electric fence. They then provoke the horse to adapt its behaviour in readiness for those things.

For example, how many horses start to whinny or bang the stable door in anticipation of being fed when a person approaches with a food bowl, an entirely human invention?

The feed bowl has become a conditioned stimulus because it predicts eating.

The feed is the unconditioned stimulus because horses have no need to learn that food is for eating!

The whinnying or stamping is the conditioned response because it prepares the horse for eating, which is the unconditioned response.

Classical conditioning can cause strong emotional associations and emotional behaviour.