don't mention it vs how's that

don't mention it

phrase
  • Used other than figuratively or idiomatically: see don't, mention, it. 

  • A polite way of responding to thanks, by suggesting that the service is too trivial or humble to warrant thanks; you're welcome. 

how's that

phrase
  • Used other than figuratively or idiomatically: see how, is, that. 

  • Used to make an appeal to the umpire as to whether the batsman is out or not 

  • Used to ask someone to repeat something 

How often have the words don't mention it and how's that occurred in a corpus of books? (source: Google Ngram Viewer )