This simile was devised by Mark Twain to account for his inability to use Edison’s new-fangled recording phonograph as a means of dictating his writing.  He clearly needed technology that could answer back.

Curious to see the devil depicted as unsmiling, as he is often shown with a menacing grin.

‘… it hasn’t any ideas and it hasn’t any gift for elaboration, or smartness of talk, (and is just) as grave and unsmiling as the devil’.

Source: Mark Twain, 5 May 1885, quoted in Autobiography of Mark Twain, H.E. Smith (ed.) (Berkeley: University of California Press, 2012), vol. I, p. 9

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