cliffhanging vs on thin ice

cliffhanging

adj

  • Suspenseful. 

on thin ice

prep

  • In a dangerous, hazardous, or delicate situation; at risk. 

adv

  • dangerously, hazardously, delicately 

How often have the words cliffhanging and on thin ice occurred in a corpus of books? (source: Google Ngram Viewer )