Sentence:  The smell, the internal workings of every human being, the shit, blood, mucus <WSD>swilling</WSD> in a bag of flesh, made him mad. He felt he was wearing the glasses the stage hypnotist had given people, but instead of seeing them naked, he saw their inner physiology, their turbulence, their death. 
Meaning of the word marked with <WSD> tags:  To move around or over a surface.