Patricia Highsmith, Strangers on a Train

"But there were too many points at which the other self could invade the self he wanted to preserve, and there were too many forms of invasion: certain words, sounds, lights, actions his hands or feet performed, and if he did nothing at all, heard and saw nothing, the shouting of some triumphant inner voice that shocked him and cowed him."

"What chance combination of shadow and sound and his own thoughts had created it?"