Well,Ive seen it first hand on deer and elk.usually was a case of the animal quartering to ,or quartering away more than one thought rathrer than it being as broadside as one thought.Also,have seen it happen in a couple of center punch insidences.I would say from experiance,to deffinately give them more time,like a gut shot incident.My old hunting parner and I years ago lost an elk he shot that he only got one lung,that was a real heart breaker.We should have given him alott longer and he would have been dead in his bed ,I think.It was dark and we got up to him.probably an hour and a half after dark and I heard him girgulling,but due to us being scattered and 2 guys that came out to help talking too much,he jumped up and took off down the other side of the ridge through a pass in sheer cliffs.We returned in the a.m. and searched and hiked etc.in super steep brushy country and he got away.Then,a couple of years later I did pretty close to the same thing and had luck on my side and mine reared over backwards going over the top of the hill and was dead to my disbelief in under a couple of minutes.Deer and elk both have an unbelievable toughness and will to survive .The can amaze you at how tough they can be on a less than perfect hit.When in doubt,never be afraid to give them plenty of time.It is hard.Of course be as concientuos as possible on the shots that you take,and practice every realistic shot that you may encounter.Steep uphill /downhill.Thats my 2 cents worth.Thanks and I hope yours are all heart shots.Merry Christmas