The "flew" is the anatomical name for dogs' upper lip.
For many years I had been curious about the origin of a sound my German Short Haired Pointers would frequently make when running with their noses near the grassy ground. Recently I could see that they were vibrating their flews. The vibration related to the familiar sound. I figure they vibrate their flews to sweep up smells from the ground.
I wonder if there is a relationship between the size of a dog's flew and its property of "nose".