Like Maryland Whitetail mentioned...the better cover you have the more you can move around,but you still have to watch for sound and your scent.I try to make very slow movements if I have to look behind me or turn my head further than my eyes can see....if I catch a Deer coming up on me I try not to move at all and only move when their head is down feedin or when they pass behind a tree or cover and they cannot see me getting ready to draw my Bow or raise my Rifle.
Like Horacio mentioned....the moment you get a scratch,take a drink of water or try not to cough a Deer will be there watching You!