"...the thingness of something becomes apparent when it is no longer functioning as it did before or it becomes dysfunctional or if it appears in an unexpected place..."
i too often feel like a slug but i must say i am very pleased my anus is not above my head and mouth, as are my friends and family.
in dutch the name for slug is ‘naaktslak’ which translates as ‘naked snail’. i’ve always thought this makes dutch people less inclined to refer to slow or unpleasant persons as slugs.
best wishes and good luck with the book!