They saw passing before and above them old men bent by age and the past burden of opera-scenery.

Some could hardly drag themselves along; others, from habit, with stooping bodies and outstretched hands, looked for doors to shut.
They were the door-shutters, the old, worn-out scene-shifters, on whom a charitable management had taken pity, giving them the job of shutting doors above and below the stage.

They went about incessantly, from top to bottom of the building, shutting the doors; and they were also called "The draft-expellers," at least at that time, for I have little doubt that by now they are all dead.

Drafts are very bad for the voice, wherever they may come from.[1] The two men might have stumbled over them, waking them up and provoking a request for explanations.

For the moment, M.Mifroid's inquiry saved them from any such unpleasant encounters.
The Persian and Raoul welcomed this incident, which relieved them of inconvenient witnesses, for some of those door-shutters, having nothing else to do or nowhere to lay their heads, stayed at the Opera, from idleness or necessity, and spent the night there.
But they were not left to enjoy their solitude for long.