Sentence:  "Nasrullah's <WSD>nickerin'</WSD>, Mr. Arthur. Somethin's wrong." / "Hell, he's <WSD>nickered</WSD> before. He <WSD>nickers</WSD> all the time!" / Robinson and Snow looked at each other, saying nothing for a moment, and finally Snow told Hancock that Nasrullah never <WSD>nickered</WSD> in the paddock. 
Meaning of the word marked with <WSD> tags:  To make a soft neighing sound characteristic of a horse.