When a corral is not available, such as on remote wilderness hunts, the horses may be hobbled and cow bells may be attached to one or more animals to keep track of them and aid in finding them in the pre-dawn darkness. The gentle, rhythmic ringing of the bells through the night lets the wrangler know that the horses are nearby and feeding contentedly.  

In contrast, bells that sound like the finale of Rossini’s William Tell Overture are generally cause for alarm and will send most wranglers shooting half naked from their tent to see what the problem is. The smartest of these animals have learned to stand stock still in the morning to prevent that infernal bell from giving away their location, thereby allowing them to evade the wrangler.  You would also be amazed at the size of a tree that a full-grown horse can successfully hide behind.