Ann... I have a question for you which is right off-topic... but you're someone who could answer! I have found dogs' faces very expressive - they show really plainly what they're thinking (it seems to me), from "oh good you're back!' to "you can't prove it was me!" to "you've got to be kidding!" Can horses' faces be expressive, or is all their expression in non-face body-language?
That's a very good question! And to a person who doesn't hang around horses much, it probably wouldn't look like horses have much in the way of facial expressions. But they actually have a lot of expression! I forget how much they exactly have, but I know it's supposed to be pretty close to how many emotions humans can express. Horses just have different facial structure and muscles, so their expressions come across differently and a bit harder to read than a humans.
But their body language is also HUGE to knowing how the horse is feeling. Expressions and body language tend to go hand in hand. Loose, wobbly bottom lip means they're relaxed, as does having a back leg cocked, and their eyes being half closed/fully closed. They're alert/curious when their heads up, ears pricked forward, eyes are bright, and no loose lip, but not tight either. Fearful, their eyes change angle (not really sure how to explain this but I'll add some pics), their lips will be held tight, they'll stand stiffly and ready to bolt in a moments notice. Aggressive is the same, except their ears will be flat back and they may gave aggressive head tosses, pawing a hoof, or threatning to nip, and a swishing tail. If you don't listen to these signs, get ready to be bit or kicked xP
These are also the more obvious signs of the horses mood. There's tons of tiny signals horses give off with their faces or body language so when working with them, you have to learn fast how to read them and know how to speak their language so that you can communicate effectively with them.
Examples:
This is the second time I ever met Jack, and the day he came to live with me. He was a rescue case and was terrified of people and would bolt often when led around and if he wasn't caught, he'd flee as soon as you entered the pen with him. And in this pic, you can see by ears and eyes and lips, that he's very unsure about this situation. His bottom lip is shorter than the top as he's holding it tight in unease/fear. His eyes look worried, and his ears are in different directions as he's unsure what he needs to pay most attention to since he doesn't know what's most likely to eat him and what is safe.
This is Sam, showing how impatient he is. Jack was being slow, so Sam got grumpy with him. His ears are all the way back and his eyes are glaring at Jack. The moment following this pic, Sam actually nipped Jack's butt. So this is a good example of a very aggressive moment.
In this pic, Jack is relaxed, but listening. It was his second farrier trim while with me. His ears are back, but not flat so he's just listening to what the lady is doing. His eyes are relaxed and in general, his face and body are telling me he's slightly unsure (head is also held slightly high) since he doesn't know the lady very well, but he also knows what's expected and is relaxed in the fact that he trusts we won't harm him in any way.
Here, Jack is very unimpressed and quite relaxed. His ears are back to listen to what I'm doing and the sounds that the bottles on him make, but aren't pinned. His head is somewhat lowered, bottom lip is a bit longer than the top lip, and his eyes are partially lidded. All signs that he's relaxed and really could care less about what I was doing to him lol.
Another pic from the first day I had Jack. His head is up, ears forward, very much alert. His whole body is sort of being held high almost a little stiff, showing that while he's curious, he's also cautious and very much ready to run if the situation is unpleasant.
Hope this helps answer your question. In the end, you can see that that expression and body language are only part of the equation. Once you put them both together, you get a very clear picture as to how the horse is feeling.
It also varies from horse to horse. Some are real troopers and won't show when they're in pain and often have the lazy/bored face. Others are real comedians and are over the top with their expressions (like Sam showing his grumpy face) and will go so far as to through tantrums when they're even slightly uncomfortable.
Honestly, horses are like a combo of cat and dog personality. Best way to sum it up really lol. And their personality effects the emotions they choose to display and when.