Horse tail knot. One custom that has been handed down through generations of Great Basin buckaroos is tying a horse's tail into a "war knot." The knot keep the horse's tail out of the way, especially when the buckaroo is roping. If the horse is switching its tail, the rope can slip under the horse's tail more easily and cause a wreck. The knot also keeps the tail out of the mud in inclement weather. How to: http://www.cowboyshowcase.com/tying-war-knots.html
Did you know? Back in the day, equestrians often didn't have time to greet and speak with all the other riders before a foxhunt... so they put ribbons in their horses' tails to communicate what otherwise couldn't be communicated while racing over the fields.