Size, spots, colour. You know, that sort of thing! Now, for your next trick, study the hoofprints and follow them! Stay downwind, and you'll be able to find it again. If you see it freeze, or move very slowly straight at it. Like most animals, it's vision detects movement best, so if you move towards it you don't appear to move much just get a little bigger. I can get very close to them in my neck of the woods and watch them for ages. Usually about 30ft or so. Practice walking quietly in the woods too. Keep your weight on your rear foot, and place your front foot on the ground heel first and roll it flat. Then transfer the weight across to it. On some surfaces, you place toes first, and on some the side of the foot. Experiment-it's not that hard, then it becomes second nature to walk quietly.