Horse trainers call this behavior "spooking." Simply put, spooking is a horse’s natural way of responding to something it perceives as threatening.

"Horses are prey animals that rely on flight as their principal means of defense," explains Eric Clark, a horse trainer in Dundee, Ill. "Anytime they perceive a threat, their natural instinct is to run away. They’re very skeptical, and prone to panic when faced with new or unfamiliar situations."

Many things can spook a horse, from seemingly innocuous objects such as a piece of trash blowing in the wind, the clanging of garbage cans, the flapping of tarps, or the mere sight of puddles, to loud noises such as thunder, trucks, motorcycles or snowmobiles. Depending on a horse’s level of fear, some spooked horses simply will duck or jump a few steps, while others will gallop away.

A horse is even more likely to spook if the equestrian anticipates that the horse might spook and rides nervously as a result, according to Dr. Dean Scoggins, equine extension veterinarian at the University of Illinois. "If your horse is afraid of mailboxes and you see a mailbox as you ride down the road and tense up because you think your horse is going to spook, he probably will," Scoggins says. "If you’re focusing on the mailbox, your horse will look at the mailbox, too. He’s going to sense your anxiety and figure there must be something in that mailbox, so he better get ready to spook."

The real problem, however, is not so much that your horse gets spooked, but how he reacts to his anxiety, says Tracy Porter, a John Lyons select horse trainer in Milton, Wis. "You can’t make a horse not be afraid," she says, "but he can learn to control his fears."

If a horse spooks, she says that’s okay, as long as he doesn’t move. But if a horse reacts by running off, that’s unacceptable.

Whether your horse bravely faces his fears or lets his anxiety get the best of him primarily is determined by your own response to your horse spooking. Typically, horse owners react in one of two extremes when their horses spook, Clark says. Neither approach solves the problem. "Either they try to force their horse to go where he is afraid to go, which just makes the horse more fearful, or they take the horse away from the scary object and therefore the horse learns that fear gets him results," he says.

Sometimes horse owners inadvertently reinforce spooky behavior in their horses, Porter says. This happens when people respond to their horse’s anxiety by petting him and telling him, "It’s OK, it’s OK." In effect, what you are telling the horse is, "Good boy for getting spooked." This serves as a reward for spooking and motivates him to react the same way in the future.

"Redirect your horse’s attention. The best approach to spooking, according to trainers, is to redirect your horse’s attention by changing his focus. "Horses are linear thinkers so that normally they can only think about one thing at a time," Scoggins says. "If you can get your horse’s mind on doing something else, he will be less inclined to react to whatever has him spooked."

Direct him to move his feet. Turn him to the right, walk him forward, turn him to the left, urge him to take a few steps backward. The instant your horse starts to relax, pet him and tell him what a good boy he is. This way you reward his bravery, not his spooking.

Use a "calm down’ cue." Porter teaches her horses a specific cue, which she uses when her equines get spooked. When she puts pressure on the rein and says, "drop down," her horses know they need to put their head down to the ground. Not only does this redirect the horse’s attention, Porter says, it also makes it harder for him to get excited about whatever has him nervous.

"Horses really can’t be excited with their head down on the ground,’ she says. "Their head is normally up when they're spooked."