The idea is that the deer will flinch. Or more to the point, wont if still alive. IF that's the case though, you don't want to be that close! A lot can happen in a hurry, and it can end up with severe hunter injury!
You want to try to walk up to them from behind, so as not to spook em if still alive. Don't be in a rush...watch for breathing...nose steam, twitches, chest expansion, etc. for a minute or two....keep the animal covered with your gun. if obviously chest shot but still alive, I will back off a bit and let them die in piece without the further trauma of a terrorizing human approaching them. if it appears they are still breathing deeply, panting, trying to get up, I prefer to give them a round to the base of the skull/ neck if possible. no wasted meat, aim the bbl to go out the underside of the neck. DO NOT get close enough for a hoof hit! But if a deer is able to start getting up on its legs...if you have it covered, don't mess around. give it another one in the boiler maker.