feces vs litter box

feces

noun
  • Digested waste material (typically solid or semi-solid) discharged from a human or mammal's stomach to the intestines; excrement. 

litter box

noun
  • A box used to provide a soiling area for (usually) pet cats, generally filled with kitty litter, sand, clay chips, etc. 

How often have the words feces and litter box occurred in a corpus of books? (source: Google Ngram Viewer )