The largest majority of the time a deer will blow at me, is when they can hear me but cannot see me. They know something is there but are not sure what. I know it sounds nuts but deer are extremely curious animals. If one blows at you, just blow back. There are a few calls on the market that make the same sound. I have kept them in my immediate area for hours while they tried to figure out what I was. Kinda fun since most of the time they are does, and where I hunt we cannot shoot them except with a bow. If one blows at you do not move, just blow back. Hopefully they will not bag ass and leave, and just sort of meander away. If they do break and run, they sound the alarm the whole time they are running. Not always a bad thing but will make for a more difficult hunt.