dumb as a post vs shit-for-brains

dumb as a post

adj

  • Extremely stupid. 

  • Utterly mute; lacking the ability to speak. 

shit-for-brains

adj

  • Extremely stupid. 

noun

  • An extremely stupid person. 

How often have the words dumb as a post and shit-for-brains occurred in a corpus of books? (source: Google Ngram Viewer )