Everyone knows the expression to do something "quietly" - that is, imperceptibly, in secret from everyone. But few people know what glanders are and how this expression appeared.
The word "glanders" came to us from Italy - there "tsappa" is called a shovel for earthwork. With their help, ditches or tunnels were dug in order to get close to fortresses, cities or castles and take them by storm. In Russian, the word "glanders" began to denote the very method of opening trenches, of which there are two.
The first method is "flying glanders". They dug from the surface of the earth under cover of a protective embankment from barrels and sacks - they were prepared in advance. But the second method was called "flap" or "quiet glanders" - they dug right from the bottom of the ditch, without going to the surface.
This was done, of course, in order to remain unnoticed - slowly and secretly, stealthily. Therefore, even now, the expression "to act on the sly" means either "slowly and imperceptibly to penetrate somewhere", or (more figurative version) "to do something quietly and unnoticed by others." (For example, "He quietly began to chop the forest for firewood, while no one sees" or "He decided to seek her location quietly - slowly but surely").
It should be noted that initially there were any negative actions in mind: intrigues, intrigues behind the back and other "subversive activities". But now this phrase is not always given a negative connotation.
By the way, over time, powder bombs began to be planted in the glanders, under the walls of the besieged buildings. This dangerous and responsible business required specialists. This is how another well-known word arose - "sapper", "the one who works in glanders."
Over time, the expression "quiet glanders" turned into "quiet glanders" (it supposedly came from the name of the horse runny nose) or even "quiet glanders". I mean, a person who is so passionate about his work that, imperceptibly for himself, quietly snoring from zeal. But dictionaries do not recognize this newly formed phraseological unit and this version is considered exclusively colloquial.
