Why does saliva on the finger give correct direction of wind? When we lick a finger and put it up in the air, the side that is cooled is the one facing the direction from which the wind is blowing. But consider this, if we take a cross section of the finger, ie look at it from above, we see the wind blowing at our finger and our finger can be considered to be a cylinder.
From examples like vortex street forming around a cylindrical object, we know that a low pressure exists behind the object. Lower pressure would normally help saliva evaporate faster and thus from this point of view one would expect that the side of the finger away from the wind would evaporate faster.
What is the explanation to this?
 A: First, the reason why the finger becomes more wind-sensitive with some saliva isn't that the saliva evaporates but because the saliva, or water, is a good thermal conductor. The finger has to be warmer than the air so the heat flows from the finger to the air and a good thermal conductor such as saliva helps this flux to take place.
Second, because it's the temperature and not evaporation that matters, we must care about the temperature of the air because this is what is actually cooling the finger. Without any wind, the human body – which is warmer than the air – creates a thin layer of warmed air in the very vicinity of the skin which acts as a thermal insulator and slows down the cooling of the human body.
But the wind disrupts this insulating layer on the front side of the finger and the cooler air gets directly in contact with the finger (or the with saliva on the finger). The air on the opposite side of the finger is either stuck in vortices – that may keep on recycling some warmer air (previously heated by the finger), or if there are no vortices, the air on the opposite side of the finger is still warmer because it was heated up by the finger "recently" when the air was flowing around the finger.
A: The percentage by which the pressure lowers on the leeward side of your finger is minuscule, so it barely affects the rate of evaporation. 
A: I think is somewhat similar to when we blow on our soup to make it cold, or not? The fluid threads lower the pressure on the broth's surface and the water passes from the liquid to the gaseous state more easily due to the lower pressure. Evaporation subtracts energy and cools the soup. 
A: What you are feeling is actually an increase in heat flux away from your finger, due to an increase in convective heat transfer from locally impinging flow in the wind direction, along with a major boost in convective heat transfer from the evaporating saliva film.
I'll explain these two phenomena below.
There is impingement flow against your finger coming from the wind. This results in a locally thin boundary layer on the site of impingement, thus increasing convective heat transfer because thinner boundary layers provide less resistance to heat flow.
Furthermore, when you lick your finger, you create a thin evaporating film which increases convective heat transfer even more; a thin layer of evaporating fluid provides a small resistance (it's a thin layer) plus a large latent heat of evaporation required to evaporate. Your skin provides this latent heat.
