I always try to stop deer I shoot at with a grunt or bleat. However this is not always practical, I recently read an article by Randy Ulmer where he explains how Caribou sometimes will not stop moving. Sometimes you will need to be able to make a shot on a moving animal. He does stress that this is only acceptable at close range on slow moving animals. One of the best shooters in the world limits himself to 25 yds on slow moving game. He explains that a shaft moving 280fps will permit an animal walking at 20 yds. to cover nearly a foot from release to impact. The article is in this months Bowhunter and its called Tough Shots.