The electric shock, as punishment for entering the wrong box, came as a surprise. At times an individual would persistently attempt to enter, or even enter and retreat from the wrong box repeatedly, in spite of the shock. This may have been due in some instances to the effects of fright, but in others it certainly was due to the strength of the tendency to follow the course which had been taken most often previously. The next effect of the shock was to cause the animal to hesitate before the entrances to the boxes, to run from one to the other, poking its head into each and peering about cautiously, touching the cardboards at the entrances, apparently smelling of them, and in every way attempting to determine which box could be entered safely. I have at times seen a mouse run from one entrance to the other twenty times before making its choice; now and then it would start to enter one and, when halfway in, draw back as if it had been shocked. Possibly merely touching the wires with its fore paws was responsible for this simulation of a reaction to the shock. The gradual waning of this inhibition of the forward movement was one of the most interesting features of the experiment. Could we but discover what the psychical states and the physiological conditions of the animal were during this period of choosing, comparative psychology and physiology would advance by a bound. If the conditions at the entrances of the two boxes were discriminable, the mouse usually learned within one hundred experiences to choose the right box without much hesitation. Three distinct methods of choice were exhibited by different individuals, and to a certain extent by the same individual from time to time. These methods, which I have designated _choice by affirmation_, _choice by negation_, and _choice by comparison_, are of peculiar interest to the psychologist and logician.