Sentence:  “... I rigged up a kind of <WSD>mannikin</WSD> with old coats and a cushion—something to cast a shadow on the blind. All you fellows were used to seeing my shadow there in the small hours—I counted on that, and knew you'd take any vague outline as mine.” 
Meaning of the word marked with <WSD> tags:  A three-dimensional figure, dummy or effigy representing a man or person.