There are two other scent glands in operation at the time of the snort alert that deer make. The tarsal gland and the Inter-digital gland are both stomp activated. Those scents leave a long lasting warning of danger in that area.
"Normal" amounts of inter-digital gland scent is placed during every step the a deer makes. Too much of it placed at one time is a sure sign to deer of something amiss. Following deer that wind the "intense" inter-digital scent will alert and bound away, generally in both the direction in which they came and at right angles thereto.
Deer, like dogs, have a sense of smell that is orders of magnitude greater than man's (unverified to be 150,000 x greater). Equipped with just that defensive "arsenal" alone at their disposal it is no wonder that they alert when we are still or think the wind is in our favor.