ax to grind vs trigger point

ax to grind

noun
  • A grudge or grievance, with implications of confrontation. 

  • A proposition or point of view to advocate, especially motivated by self-interest. 

trigger point

noun
  • An event, arrangement, provocation, etc. that leads a certain, generally violent or angered, action to be taken. 

  • A hyperirritable spot in the skeletal muscle; a point in tender muscle that tends to elicit pain upon pressure or touch. ᵂᵖ 

How often have the words ax to grind and trigger point occurred in a corpus of books? (source: Google Ngram Viewer )