That happened to my adopted brother a couple of years ago. He had a great shot on a monster of a buck and took it. He hit the buck and it fell, then got up. Well is was starting to get dark and he started to follow the blood trail and it went for 50 or so yards and then stopped, well he looked and looked. He looked for I think an hour and couldn't find it. Well he gave up because it was too dark and in a remote hard to get to location. Well as it turns out they found the buck about 6 months later. It was about another 50 yards from where the blood trail stopped in an aera of very heavy brush. My brother told me it made him sick that they couldn't find it that night. That was the only deer he had a shot at during the season. It sucks and I hope I have better luck than that this year because I am hunting in his spot this year since he is in Kuwait. I promised him 10 pounds of deer jerky for Christmas. I better make good on that promise. Thanks Arvin