send shivers down someone's spine vs unnerve

send shivers down someone's spine

verb
  • To terrify; to make someone feel extremely nervous. 

unnerve

verb
  • To make somebody nervous, upset, alarm, shake the resolve of. 

  • To deprive of nerve, force, or strength; to weaken; to enfeeble. 

How often have the words send shivers down someone's spine and unnerve occurred in a corpus of books? (source: Google Ngram Viewer )