When a horse is cinched to tight this is what can happen. Google Endospink, a race trainer who uses this to his advantage to lay horses down. He deals with real crazies and laying them down takes the stupid out of them. When cinching, the horse should be walked 5 or 6 strides, then retightened but so one can get all four fingers in. The walking prevents them from holding their breath. By four fingers, I don't mean you really have to push to get them between cinch and horse but with a little effort.