Bag of Mystery (sausage)

Entry in progress—B.P.
   
(Oxford English Dictionary_
bag of mystery  n. (usually in pl. bags of mystery) slang a sausage or saveloy.
1864   J. C. Hotten Slang Dict. (new ed.) 69. 
1879   W. J. Barry Up & Down xvi. 163   A slice of bread was given with the ‘bag of mystery’, as some rowdies called the luscious saveloy.
     
28 February 1869, Lloyd’s Weekly London Newspaper (London, UK), pg. 11, col. 1:
THE BETHNAL-GREEN SAUSAGES.—(...) It was an unlucky day for the brothers Simmonds, of Russia-row and Hans-place, Bethnal-green, manufacturers of those bags of mystery sausages, when Mr. Burrowes, the sanitary inspector, took possession of the mass of unpleasantness.
 
23 October 1869, Fun (London, UK), pg. 74, col. 2:
A Derivation.
IN a police court the other day sausages were defined as “bags of mystery.” Let us see—the Greek is “mew-sterion,” of course.
 
4 December 1869, The Daily Evening Telegraph (Philadelphia, PA), pg. 6, col. 3:
A DEFINITION.—In a police court the other day sausages were defined as “bags of mystery.” Let us see—the Greek is “mew-sterion,” of course.
 
Google Books
Cassell’s Dictionary of Slang
By Jonathon Green
London, UK” Wiedenfeld & Nicolson
2005
Pg. 57:
bags of mystery n. (also bag of mystery, mysteries, mystery, mystery bags) [mid-19C] sausages or saveloys, [their dubious constituents, note RN use mystery torpedoes, links of love; British Army use spotted mystery]
 
Twitter
Andy Perkins
@oaldoak
Replying to @WalthamRabble
Sausages… or what my would have said, “Bags of mystery!”
3:55 AM - 7 Oct 2018