Here in Kentucky, we don't have a lot of Hemlocks like you all do in the mountains but we have a lot of deadfalls hanging in the tree tops. A couple years back, hurricane Ike came through and there are a lot of trees and big chunks of trees hanging in the tops of trees that didn't blow over. These are just waiting for the right gust of wind to come along and send a 400 pound branch crashing to Earth.
That age old question "if a tree falls in the forest and nobody is around to hear it, does it still make a sound?" is a question I'd just as soon leave unanswered.
Hey, thanks for the reminder though. My son and I will be in the Mountains next week and it's always a good idea to be aware of what's hanging over your head as one works his way upstream.