The NonVerbal Dictionary of Gestures, Signs & Body Language Cues

Clever Hans Phenomenon

Conceptual model. The hypothesis--also known as expectancy communication or interpersonal expectancy effects--that a person's nonverbal communication unwittingly scripts a recipient's behavior, deportment, or performance in the manner of a self-fulfilling prophecy.
Usage I: Displayed nonverbally, a teacher's positive expectancies for certain chosen students encourages them to work harder and get better grades.
Usage II: A judge's body language can transmit negative signals (e.g., gaze cut-offtense-mouth, and tongue-show), which may inadvertently influence jurors to decide against a defense attorney's case.

Salesmanship. "As in most areas concerning the sales confrontation, the salesperson will be viewed and treated largely according to how he expects to be treated" (Delmar 1984:31). 

Clever Hans. As primates we are highly responsive to nonverbal cues, and thus susceptible to the "Clever Hans" phenomenon (Pfungst 1911):

Once upon a 19th-century time, there lived a world-famous horse named Clever Hans, who displayed amazing mathematical ability. If somebody asked him to add, say, five plus seven, Hans would faithfully stomp 12 times, astounding all present. For years, puzzled scientists were baffled by how the animal could add and subtract. One Oskar Pfungst solved the riddle at last. According to Pfungst, Clever Hans looked closely at his human audience for subtle body cues [e.g., of the eyes and head] telling him when to stop tapping his hoof. Tinykinesic signs alone sufficed (Givens 1981:56).
RESEARCH REPORTS1. Research has shown that "nonverbal cues play an enormous role in signaling interpersonal expectations, often within the first 30 seconds of an interaction" (Burgoon et al. 1989:448). 2. Relaxed postures, dominance displays, leg movements, head-nodding, smiling, and "interested" facial expressions may show positive expectations; while head-shaking, eyebrow-raising, looking surprised or disappointed, and tapping a pencil may show negative expectations (Burgoon et al. 1989).