Hearing and Sense of Smell
When Lunging a domestic horse, it will often have the inside ear cocked toward you, while the outside ear is pricked, indicating that the horse is concentrating and listening.
Horses in the herd will observe the ear movements of their fellows and react accordingly. Their sense of smell is also highly developed.
In the wild, the sense of smell allows the stallion to identify mares in heat, as well being able to smell rival stallions through their dung, which is an important form of communication.
Perhaps the most interesting of the senses is, however, the horse's keen vision.