Tinbergen's careful description of the courtship dance highlighted several important features of mating behavior. The dance was complicated, but it comprised a series of quite simple steps. Each step involved a specific stimulus from one fish followed by an equally specific response from the other. Fin the type of response depended not only upon the stimulus but also upon the physiological state of the fish. For example, the color red was an important stimulus, but it caused different responses in males and females, Males would attack red-colored models, even those that did not look like fish. Gravid females would follow these same unrealistic red models through the zigzag courtship dance, even if a nest was not present.