Like others have said it is the movement, I have shot deer and turkeys not long after having a smoke and I have also been busted , I remember thinking ah nothing around I will have a smoke after lighting it and looking up to a couple white tails headed the opposite way, I am sure all smokers have been busted while not even knowing it. The less you do while in the stand the better the odds of a successful hunt, although most smokers are willing to take the risk.
