As she watched the white bobbing against the dark water she realized she had finally done it, she had hit bottom. She was littering. -- (pg. 381)
avidity (pg. 114) -- Ardent desire or craving; eagerness.
Scars on the outside simply kept score; it was the scars on the inside one had to watch out for. (pg. 63)
Under certain circumstances crime could be considered a career choice. Littering was just a character flaw. (pg. 227)
Not for the first time, she was glad she never went anywhere without her library card...She made a mental note to suggest to the Estes Park librarian that the cards be made with at least one good slashing edge. (pgs. 170-171)
Spavined (pg. 76) -- Probably means old and decrepit here.
Hellmouth (pg. 76) -- A site of massive supernatural activity.
Megrims (pg. 83) -- A state of depression.