A brief description of the behavior of the dancer in the brightness discrimination experiments which have been described may very appropriately form the closing section of this chapter. For the experimenter, the incessant activity and inexhaustible energy of the animal are a never-failing source of interest and surprise. When a dancer is inactive in the experiment box, it is a good indication either of indisposition or of too low a temperature in the room. In no animal with which I am familiar is activity so much an end in itself as in this odd species of mouse. With striking facility most of the mice learn to open the wire swing doors from either side. They push them open with their noses in the direction in which they were intended by the experimenter to work, and with almost equal ease they pull them open with their teeth in the direction in which they were not intended to work. In the rapidity with which this trick is learned, there are very noticeable individual differences. The pulling of these doors furnished an excellent opportunity for the study of the imitative tendency. When confronted with the two entrances of the electric-boxes, the dancer manifested at first only the hesitation caused by being in a strange place. It did not seem much afraid, and usually did not hesitate long before entering one of the boxes. The first choice often determined the majority of the choices of the preference series. If the mouse happened to enter the left box, it kept on doing so until, having become so accustomed to its surroundings that it could take time from its strenuous running from _A_ by way of the left box to the alley and thence to _A_, to examine things in _B_ a little, it observed the other entrance and in a seemingly half-curious, half-venturesome way entered it. In the case of other individuals, the cardboards themselves seemed to determine the choices from the first.