How would a gifted writer describe picking her nose?

I'm glad you asked! Here's Sylvia Plath on mining for nuggets:

There are so many subtle variations of sensation. A delicate, pointed-nailed fifth finger can catch under dry scabs and flakes of mucus in the nostril and draw them out ot be looked at, crumbled between fingers, and flicked to the floor in minute crusts. Or a heavier, determined forefinger can reach up and smear down-and-out the soft, resilient, elastic greenish-yellow smallish blobs of mucus, roll them round and jellylike between thumb and forefinger, and spread them on the under-surface of a desk or chair where they will harden into organic crusts. How many desks and chairs have I thus secrtively befouled since childhood? Or sometimes there will be blood mingled with the mucus: in dry brown scabs or bright sudden wet red on the finger that scraped too rudely the nasal membranes. God, what... satisfaction! It is absorbing to look with new sudden eyes on the old worn habits: to see a sudden luxurious and pestilential “snot-green sea,” and shiver with the shock of recognition.

From Plath’s Journals, via Janet Malcolm’s The Silent Woman, 160-161.