I have heard, (and tried last year with success) that if a deer snorts and spooks without actually SEEING you or they arent 100% sure what it is that spooked them then do a snort back at them. I have read that deer snort sometimes to vocalize to other deer just to know where other deer are.
Last year I had a deer spook for no reason I can find, and when he did he ran about 30 yards and stopped. He was behind a thicket and so I got out the buck roar by primos, gave a snort back at him, and within 2 or 3 minutes he came right back to where he was. Stood around and ate for a bit and then left after 10 minutes or so.

I'm not guaranteeing that it works everytime. Hell, I'm not 100% sure that it worked for me, but it sure seemed so. Its worth a shot anyways. All i knew was he snorted, I snorted back, and here he came back. You be the judge.