A simile is a figure of speech that metaphorically compares one thing, person, place, element or idea to another while using the words "as", "such as" and "like." It is often used to make the writing or the speech more colorful, interesting and memorable.
The word "chin," and the sentence "the corner of her mouth glistened with wet" helps us infer that the simile "which inched like a glacier down the deep grooves enclosing her chin" wants to convey that the woman is drooling (the glacier is the saliva).
