constrain vs put the frighteners on

constrain

verb
  • To force physically, by strong persuasion or pressuring; to compel; to oblige. 

  • To keep within close bounds; to confine. 

  • To reduce a result in response to limited resources. 

put the frighteners on

How often have the words constrain and put the frighteners on occurred in a corpus of books? (source: Google Ngram Viewer )