fremd vs rare as hen's teeth

fremd

adj
  • Strange, unusual, out of the ordinary; unfamiliar. 

  • Not kin, unrelated; foreign. 

noun
  • A stranger; someone who is not a relative; a guest. 

  • An enmity. 

rare as hen's teeth

adj
  • extremely uncommon 

How often have the words fremd and rare as hen's teeth occurred in a corpus of books? (source: Google Ngram Viewer )