The horse's hearing is much more acute than our own. He has large, mobile ears, operated by ten muscles (humans have three; cats have 32), which can rotate fully, and can pick up sounds from all directions. They operate in conjunction with the eyes. In other words, when an ear is pointed forward, its corresponding eye is also pointed forward. Tradition says that the closer together the set of the ears; the better the forward vision. The ears are one of the best indicators of a horse’s mood, giving crystal clear messages because they are so mobile. They can be rotated almost 180 degrees and move independent of each other. Ears that are actively moving in all directions indicate a horse that is attentive to all around him. Ears that are almost flaccid belong to a relaxed horse. The ears are held forward when the horse is interested, pricked rigidly forward for anxiety, twisted toward sounds to listen, and laid back tightly against the top of the neck to show displeasure or aggression. If his ears are laid back against his head, use extreme caution working around him until he’s calmed down.
Horses have large ears that can twist almost all the way around. The ears will tell you the direction of the horse’s attention. They can listen to two directions at the same time. Their hearing is very sensitive. Like other prey animals, the horse's ability to pinpoint sound is not very precise. He knows the general direction of a sound; enough to know which way to run! His hearing range is greater than ours: 55 to 33,500 hertz as compared to 30 to 19,000 hertz (cycles per second) in humans. His bottom range is higher than ours which means he may not hear you talking if your voice is pitched very low, and his top range is higher as well: he may spook at an unfamiliar sound which you can't hear.
The picture shows more than just ear direction. It also shows body language. The horse at the back is not relaxed; he’s listening with his whole body to the horse in the front. The horse in front is listening to the horse behind and to the camera.