From what I have read, if you're attacked by a Grizzly, play dead. If you're up against a Black Bear, fight back with whatever you can get your hands on. I'm assuming this is due to size variances between the Grizzly and the Black Bear. But from what I have seen on most websites related to this subject, the idea's range from staying quiet to soft talking to yelling loudly and from standing still to running like the wind.