call of nature vs shitting

call of nature

noun
  • The bodily urge to urinate or defecate. 

shitting

noun
  • The act of defecating. 

adj
  • An intensifier, often applying more to the whole utterance than to the specific word it modifies; same as fucking. 

How often have the words call of nature and shitting occurred in a corpus of books? (source: Google Ngram Viewer )