The key is to get one of those "what's up doc?" calls. You know the kind very similar to the can call, but you have to be careful. They are indeed ferocious and they come in fast. I prefer a frontal shot as they're climbing up the tree to get you. Very important to bring a carrot along as back up in case you don't get the shot off. Just hand them the carrot and say "what's up doc?". Works everytime. I've been spared many a time by doing so.