researchers have also developed terms to describe the scratch reflex movements themselves. a "pure" movement is one in which only one form of the scratch response is utilized to respond to the stimulus. a "switch" movement occurs in a transition zone, and is characterized by the smooth switching between two different scratch forms in response to the stimulus. a "hybrid" movement is observed and occurs at transition zones as well, and is characterized by two rubs during each scratch cycle, where each rub is derived from one pure form movement. research on hybrid and switch movements at transition zones indicates that the cpgs responsible for scratch generation are modular and share interneurons. for this reason, in both the switch and hybrid movements, the path of the moving limb is smooth and uninterrupted.