Here is how Fred said it ...
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Get out of the line of sight.  I'm going to let you think about that......

Stand vs Sit. You blend in much more standing against a tree vs sitting at the base of one. Ever since I started doing that, I've have been busted by far fewer deer in the woods. The other thing is a good face covering, and if they look at you, keep one eye closed and squint out of the other. 2 eyes next to each other are never a good thing.

I was coming back to mention about the 'eyes' before seeing the previous poster mentioned it. While most people would consider the premise highly questionable....I do believe that deer (like people) have an undefined sense that they are "being watched". I never look at a deer dead on until it is time to shoot; much preferring to watch in my side or indirect vision. Squinting seems to help as well.

Yes sir if you want to get busted make eye contact with a deer I don't care how good you are hidden if they see 2 eyes they are headed to the next county!!!