cocoon vs curtain off

cocoon

verb
  • To envelop in a protective case. 

  • To withdraw into such a case. 

noun
  • The silky protective case spun by the larvae of some insects in which they metamorphose, the pupa. 

  • Any similar protective case, whether real or metaphorical. 

curtain off

verb
  • To isolate. 

  • To separate, isolate or block by means of a curtain or other barrier. 

How often have the words cocoon and curtain off occurred in a corpus of books? (source: Google Ngram Viewer )