locket vs pearl necklace

locket

noun
  • A pendant that opens to reveal a space used for storing a photograph or other small item. 

  • A small white marking on a cat's coat. 

pearl necklace

noun
  • Used other than figuratively or idiomatically: see pearl, necklace. 

  • A sexual act whereby semen is ejaculated onto a partner's upper chest, breasts and/or throat. 

How often have the words locket and pearl necklace occurred in a corpus of books? (source: Google Ngram Viewer )