Horses are fluent in body language. It's the main way they talk to each other--and to us. If we want to understand our horses better, we should become as skilled at reading equine body language as we can.
British zoologist Desmond Morris talks a lot about body language in his classic book Horsewatching. The movement of your horse's head and neck, for example, can express irritation in various ways. There's the head shake (a sideways back-and-forth); the head toss (an upward flinging); and the head jerk (an up-and-back movement). Each of these actions are used to chase away flies, of course, but they're also used to express irritation at something else, such as another horse or a human.
In either case, your horse is signaling frustration at being bothered by something.
"This is the equine equivalent of a human scratching the back of his head when he is angry," Morris writes. "Like horses, we perform a primitive 'irritation reaction' to a new form of irritation that is now completely in the mind. The people who infuriate us are not actually stinging the skin on our heads and yet we behave as if they are."
He cautions that a horse's irritation-based head-tossing and -shaking are not to be confused with head bobbing, where the head is repeatedly raised and lowered to improve a horse's close-up or distance vision.
Forward movements of the head are your horse's way of asserting himself, says Morris. Head thrusting and head lunging
(the latter presumably having the movement of the whole body behind it) are aggressive actions usually related to biting. By contrast, nose nudging, performed with the top of the nose and with the mouth closed, is "a milder display and says little more than 'Hey, what about me?' or 'Come on, let's get on with it.' It demands attention and is used with both horse and human companions," the author writes.
Morris defines neck wringing (in which the whole neck is twisted this way and that) as either a playful interaction that says "I want to go in all directions at once," or an unhappy expression of "I want to get out of here."
In my own experience, neck wringing seems also to be a way that a horse--especially a mare--says "I'm a tough guy. Don't underestimate me!"
What types of head-and-neck body language have you observed in your horse?