The nostrils are moist and mobile. The folds on each side, shown here, allow them to move and expel air. They quiver and rotate in order to seek out the direction of a scent. The moisture aids the nose in detecting scent. If scent is airborne, the dog raises her nostrils to the breeze, if it is buried in the ground, those nostrils can often come up with a nose-full of dirt.