Aside from the fly issue, the tail can also be an integral part of a horse's body language . It is usually used to indicate extreme feeling (an exclamation point of sorts, if you like - I do :o)
Swishing - (not at flies) Angry, extremely aggravated or total happiness/euphoria.*
Flagged - Extreme fear (when running) or utter delight (together with a head bob while trotting/prancing in circles or other patterns; a full-body celebration).**
Clamped - Fright (usually precedes a kick; they may just drop their derriere and scoot) or if feeling cold and/or wet.
* Visit our website and watch the video clip of Blue Horse Matinee on our Horse Heroes page to see some of those happy swishes in action :o)
**Some breeds have a higher tail set (see Lady's photo, above) and consequently offer a more intense version of the "flag". Both Bella and Shadow's tails will flip all the way upside down at these times (there is a photo of this further down).
Casual vs. Clamped
There is usually a small space under the horse's tail (L). The horse on the right has his tail clamped due to cold (if it is due to fear, it is usually a precursor to either bolting or kicking).
Comparing The Tail Set
These two horses have different tail sets. While both horses are trotting and each has raised his tail slightly, the horse on the right has a higher tail set. If I was going to guess, I'd peg the horse on the left as a Quarter Horse and the one on the right an Arabian.
Tail Torquage: How High Will it Fly?
This photo shows a horse with his tail flipped completely over. Two of our horses; Shadow (a Tennessee Walker), and Bella (an Arabian), do this. Actually, I have been known to tell all of our horses not to get their tail in a twist over things (when asking for calm :o)
Punctuation is Crucial to Clarity: Be sure to read the complete "sentence"!
Looking at the photo on the right, note the pinned ears, pinched nostrils and tucked chin of this horse. It is easy to tell by looking at these things that she is angry.
When you add in the tail as an exclamation point, however, you can see that this mare is not merely angry she is LIVID.
Next up: Practice putting it all together with some more sample photos :o)