rare as hen's teeth vs selly

rare as hen's teeth

adj

  • extremely uncommon 

selly

adj

  • Rare; wonderful; admirable 

noun

  • A marvel; wonder; something wonderful or rare 

adv

  • Wonderfully, wondrously. 

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