piss one's pants vs shit oneself

piss one's pants

verb
  • To be extremely frightened. 

  • To laugh uncontrollably. 

  • To wet oneself; to urinate in one's own clothes while they are being worn. 

shit oneself

verb
  • To be very frightened or astonished (to the extent that one might lose control of one's bowels). 

  • To soil oneself. 

How often have the words piss one's pants and shit oneself occurred in a corpus of books? (source: Google Ngram Viewer )