Sentence:  `` The pattern '' , says Dr. Morton Schillinger , psychologist at New York 's Lincoln Institute for Psychotherapy , `` is for the husband to hover about anxiously and eagerly , virtually trembling in his hope that she will flash him the signal that tonight is the <WSD>night</WSD> '' . 
Meaning of the word marked with <WSD> tags:  the time after sunset and before sunrise while it is dark outside