skulking vs under wraps

skulking

noun
  • The action of one who skulks. 

under wraps

prep
  • In secrecy or in hiding. 

  • Of a horse: restrained from performing at its best in a race, so as to mislead others regarding its potential. 

How often have the words skulking and under wraps occurred in a corpus of books? (source: Google Ngram Viewer )