flabbergast vs leave someone open-mouthed

flabbergast

noun
  • An awkward person. 

  • Overwhelming confusion, shock, or surprise. 

verb
  • To overwhelm with bewilderment; to amaze, confound, or stun, especially in a ludicrous manner. 

leave someone open-mouthed

How often have the words flabbergast and leave someone open-mouthed occurred in a corpus of books? (source: Google Ngram Viewer )