on thin ice vs threatening

on thin ice

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

adv
  • dangerously, hazardously, delicately 

threatening

noun
  • An act of threatening; a threat. 

adj
  • Presenting a threat, posing a likely risk of harm. 

  • Making threats, making statements about a willingness to cause harm. 

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