Suggested video from David....

For this clip I rub one finger back and forth horizontally, very high on my upper gums, above my teeth. Random speeds but not too fast and not too slow. At times I go very high, as high as my finger can go, but mostly I focus on top and front part of my mouth but bottom sometimes too. At times I use more than one finger but mostly it's my index doing the rubbing. Finger licking and sucking with lip and tongue teasing with fingertips.