Horses often get banged and bruised by running into things, being kicked by another horse, falling down when running and bucking, etc. It’s not unusual to suddenly discover your horse has a large, soft lump on some part of his body. The most common areas are the hindquarters, chest, or along the ribs. The skin might not be damaged, but the injured tissues underneath can bleed or ooze serum, creating a large “balloon” under the skin. The damaged blood vessels usually don’t stop bleeding until there is enough pressure from the fluid accumulation to halt the bleeding and allow the blood to clot