Some horses have learned that by taking in a lung full of air when they are being saddled, they can avoid being squeezed by the cinch strap. The cinch strap, or saddle girth, is the wide band that secures the saddle (and therefore you) to the horse.  Whenever mounting an animal, always run a hand between the cinch strap and the animal to ensure that it’s tight.  

One time in Montana, I forgot to do this and was midway down the trail when I suddenly found myself riding on the underside of the horse and trying rather desperately to keep me and my bow from getting stomped on.   

“Are you okay?” asked the guide?  

“Yes,” I said, trying to sound like I often rode horses this way. “I just wanted to check out the undercarriage of this fine animal. Yep, it’s a gelding, just like I figured!”  Being a gelding, it is quite likely that he still held a grudge.