What is it? Plastic bags flapping in a tree? Oddly shaped objects? The hose? Flags? Balls?
Most horses will have a fear for that one odd object, especially in the beginning. It seems natural to comfort our horse. Pet them with it (well, try to at least), talk to them about it, or chase them around with it so they might just decide to accept it.
First, I never (I guess I shouldn’t say never… usually) don’t bring the object to my horse. Instead, I allow my horse to approach the object on their own. If they’re worried and snorting about an oddly shaped garbage can, I hang out and let their curiosity, which always wins, take them to it. I’ve found this to be the fastest way to allow a horse to investigate. Then I have them follow it, then I can start bringing it to them and having them relax in that scenario.
Another important part that the horse has to learn in order to overcome their fear is having them yield to the object.
The horse should not just be tolerating the object – we want them to accept or become desensitized to it. Let’s say we have a stick (whip, etc) with a flag or plastic bag tied to the end. It’s usually not enough to just pet them with it forever. In that case the horse will just stand there, perhaps collecting nervous energy and not releasing it, and tolerate it. But it’s still something they worry about – if a plastic bag jumped out of the bushes, they would jump with it.
So we have them yield. I might wiggle the flag at their hind quarters and right when the horse moves them, I rub them with the flag. This shows the horse that they can start something with it. They know what to do when they see a flag flapping at them. Or we wiggle it in front of them as we ask them to back up and then rub with it again. This simple exercise can excel their desensitization immensely.
Remember: desensitize, don’t teach them to tolerate.