I dont think anyone will ever know what spooks a deer. I have driven my 4-wheeler right up to stands and had deer walk out not 5 mins later. Hell my farmer sees more deer than I do when driving around his loud ass combine. But if I sneeze I scare everything away for 10 miles. I have friends that smoke in the stand and have shot bigger bucks than me while I sit there and dont move an inch or make a noise and never see a thing. I just think some people just have better hunting Karma. I must have pissed someone off cause I havent fired my rifle at a deer in a month.