shit-for-brains vs smooth-brained

shit-for-brains

adj
  • Extremely stupid. 

noun
  • An extremely stupid person. 

smooth-brained

adj
  • Stupid, foolish; ignorant. 

  • Lissencephalic; having a brain which lacks convolutions due to malformation. 

  • Having a brain which is naturally smooth in appearance. 

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