There are some sounds that are primordial; example, if you’re in a dark room and someone racks a shell into a 12 gauge pump you don’t need to be a gun expert to know what just occurred. It’s time to get on the floor....
Really? Just making it easier for the perp to kill you, all nice and stationary? If you hear a shotgun being racked or the charging handle being released, it's time to start moving - either at him, if he's close enough, or away to the first cover you can find.
Really bad advice, buddy.