And when you've read all the answers and think they must be right..... there are exceptions. The correct answer is experience. Follow every blood trail..... even if you saw the deer fall. Example of where all the answers can be wrong. I slammed a buck at close range from above. I saw the hole appear in the deer about 5 ribs up angling forward. The deer ran off.The arrow was covered with green slime... not blood, but green slime. The deer went about 80-100 yards. The arrow had entered the near lung, passed through the food pipe, hit the other lung and exited under the offside armpit. There was maybe at most a tablespoon of blood for the whole trail. Upon autopsy I found a glob of cud about the size of a small apple between the skin and chest wall under the armpit. The arrow had hit both lungs and was all green slime. No blood. My buddy insisted I gut shot the deer. We found the deer by following just the tiny little drops, foot prints etc. It was a perfect shot except for the fact the deer reguretated his cud into the exit hole. The arrow must have caught him bringing up a cud or swallowing a large bush... at any rate... everything was green and it was a perfect hit. Experience and observation are your best teachers. Patiences and attention to detail are your lessons.