“Slang” is a cant term used for a travelling show in 19th-century Britain. By extension, in the jargon of travelling marionette showmen, “slangs” became a term for the strings of a puppet and “slanging” for the way in which the strings were attached to control bars.  

Mayhew’s fantoccini man mentions how he rapidly put away a puppet after a performance so that people could not see how it was strung, and this notion of secrecy was carried even further by Thomas Holden and others who would not allow any outsider backstage during a performance.

The French term “ensecrètement” (making secret or vow of secrecy) is a similar term of the métier to describe how a puppet is strung.

(See also Ensecrètement, Secrecy, String Puppet, Travelling Puppeteers.)