Prunes and prism was coined by Charles Dickens. It first appears in Book 2 Chapter 5 of "Little Dorrit".

'Papa is a preferable mode of address,' observed Mrs General.
'Father is rather vulgar, my dear. The word Papa, besides, gives
a pretty form to the lips. Papa, potatoes, poultry, prunes, and
prism are all very good words for the lips: especially prunes and
prism. You will find it serviceable, in the formation of a
demeanour, if you sometimes say to yourself in company--on entering
a room, for instance--Papa, potatoes, poultry, prunes and prism,
prunes and prism.'

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