I was grooming my 20 y/o quarter horse this morning, and when I ran the curry comb over his lower ribs and abdomen only on the left side he pinned his ears back and swung his head around towards me. I palpated this area with my hand using moderate pressure, and again it caused him distress. Of course my first thought is possible colic, but he is showing no other signs or symptoms at all. This is my first horse, so I honestly don't know much about the progression of colic. Could it be an early sign? Or without any other symptoms, could he have a bruised rib?