I have one very experienced field trial horse who is wonderfully reliable, athletic, smooth and anyone can ride him. BUT, once in a while, I'll detect some nervousness or tendency to booger for no reason over some object. I may ride him ten days in a row for half a day and never have a problem. He may have actually passed the same spot six times during a three day field trial but for whatever reason he isn't in the same place mentally and you can feel him tense up. I have some keys I use including my voice to keep him somewhat calmer and we usually slide by the booger without incident. Sometimes, I am handling or scouting and really need him to just drive right thru so I can do my job. This usually works out OK but I have to be aware of not only my job but the 1200 pounds that I'm sitting upon! 98% of the time he is concentrating on his job and helping me go after the dog, etc. When he's in that 2%, I need to be aware of his state of mind if only for just a few seconds and we'll both be happier overall.
You can feel this in your horse once you are aware enough of each individual animal. A better rider than myself may feel this quicker or earlier than I do but knock on wood, I continue to get by as I learn...There are no perfect horses just as with dogs and people but being aware might keep you healthy in the case of your vulnerability six feet in the air. If he wants to avoid something, work it out slowly unless you are the real deal horse trainer and rider. Saves you some time in the hospital. Be safe first!