dropping vs litter box

dropping

noun
  • A piece of animal excrement; dung. 

  • The act of something that drops or falls. 

  • Something dropped; a droplet. 

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 dropping and litter box occurred in a corpus of books? (source: Google Ngram Viewer )