pick at vs pinch off

pick at

verb
  • To touch, grab, handle, or pull tentatively or gingerly, using a utensil or one's fingers. 

  • To pick on or repeatedly criticize (someone). 

pinch off

verb
  • To separate (something) from something else, using a pinching motion. 

How often have the words pick at and pinch off occurred in a corpus of books? (source: Google Ngram Viewer )