To flow against or along
A fleshy portion of the mouth
bite one's lips
hang on the lips of
keep a stiff upper lip
smack one's lips
Her lip began to tremble.
She nibbled on her lower lip, thinking furiously.
Her face had shriveled, her upper lip had sunk in, and her eyes were dim.
He glanced at her and his lip twitched.
He touched his lip with his tongue.