From page 178: The pattern of startle (which has been studied by high-speed photography) is remarkably regular. It begins with an eye-blink; the head is then thrust forward; the shoulders are raised and the arms stiffened; abdominal muscles shorten; breathing stops and the knees are flexed.
The startle pattern is a model of other slower response patterns: fear, anxiety, fatigue and pain all show postural changes from the norm which are similar to those that are seen in startle. In all of them there is a shortening of neck muscles which displaces the head, and which is usually followed by some kind of flexion response, so that the body is drawn into a slightly smaller space. As in startle these postural responses cannot take place without the prior displacement of the head and the shortening of neck muscles.