Sentence:  Then Nathan Eldred, gently pushing, was muttering, ‘On you go, dear. Good luck!' and she was edging between the <WSD>tormentor</WSD> and the backing flats, in front of the curtain, holding her small hands out to the sudden-silenced audience ... 
Meaning of the word marked with <WSD> tags:  One of a pair of narrow curtains just behind the front curtain and teaser that mask the areas on the sides of the stage and can be adjusted to the desired width.<ref>W. P. Bowman and R. H. Ball, "Theatre Language: A Diction of Terms in English of the Drama and Stage from Medieval to Modern Times", New York: Theatre Arts Books, 1961, p.(nbsp)395,[https://catalog.hathitrust.org/Record/001111243]</ref>