I put back shoes on a horse that was 7 years old and had never had hind shoes on before. He kicked himself while stomping flies. It was on the front of the hind cannon, right over bone only area. I did notice a hard swelling with slight heat and felt it with my hand at the time. It did not seem to have broken the skin, just caused a lump. I felt it every day for three days, and it cooled down. Then I forgot about it. Seven days later it was swelling and warm. Called vet ASAP. Cellulitis.