We can understand also the horse's never-flagging attentiveness when we recall that self-preservation prompts eternal vigilance over against all that is going on in the animal's environment. (In the case of Hans, hunger was at first the motive; later, habit did the work.) Furthermore, the lower form is not hindered in giving itself over to its sense-impressions by the play of abstract thought which tends so strongly to direct inward our psychic energy,—at least, in the case of the cultured.
Nevertheless, Hans still remains a phenomenon not only in excelling all his critics in the power of observation, but also in that he is the first of his species, in fact the first animal, in which this extraordinary perceptual power has been proven experimentally to be present. It has long been known[55] that horses could be trained to respond to cues in the form of slight movements, which remained unnoticed by the layman, and this fact has been made use of by circus trainers to its fullest extent. But such signs, I have discovered, are without exception, of a far coarser sort than those we have here described, and they can be instantly detected by the practised observer. Nor was it known to professional trainers that it was possible for the master to direct a horse to any point of the compass simply by means of the quiet posture of the body. For this reason it was believed that no signs could possibly be involved in the color-selecting-tests (cf. [Supplement III, page 255]). In this we have the support of some of our experts, as is witnessed by the following extract from a letter of his Excellency Count G. Lehndorff, one of our best hippological authorities, who at one time carefully examined the Osten horse. (The letter was addressed to Mr. Schillings, and I have permission of both gentlemen to use it). In it he says: "If the author's statements, in which you also have concurred, are correct, and if, as a matter of fact, the horse really does react to such minute movements as are absolutely imperceptible to the human observer, then we have indeed something quite new, for hitherto no one would have believed that horses can perceive movements which man cannot. But I am even more surprised by the explanation of the color-selecting feats.—This too, is something absolutely new. One would not have deemed it possible that a horse could do anything of the kind simply by using the posture of a man's body as a cue to which it could react with such precision."
And yet, even though both facts were new concerning the horse and had not hitherto been proven experimentally regarding any other species, nevertheless something of this sort has been known concerning the dog for some time. His ability to single out an object upon which his master had intently fixed his gaze, was made the basis of a special form of training, called "eye-training,"[56] nearly one hundred years ago. The dog was taught to focus constantly upon his master's eyes and then upon command to select the object which he, the master, had been fixating. Such a dog has been described by the naturalists A. and K. Müller.[57] But the master of the dog, unlike Mr. von Osten, would not permit anyone else to work with the animal, and the two brothers, recognizing the trick, were justified in adding that "the whole affair aimed at deceiving the public, and the dog's reputation was but a means of making money". The success of such exhibitions appeared furthermore, to depend upon the close proximity of the trainer and the dog, whereas the direction of the head (and even of the body) could very probably be perceived at greater distances also. At least we learn from a reputable source that in the hunt, dogs can perceive from the mere posture of their master, what direction he intends to take.[58]
But a still more curious fact is this, that dogs, too, learn—evidently spontaneously—to react to the minimal involuntary expressive movements of their master. The first example mentioned in the literature on the subject is that of an English bull-dog called Kepler, belonging to the English astrophysicist, Sir William Huggins.[59] We are told that this dog seemingly could solve the most difficult problems, such as extracting square roots and the like. The numbers were indicated by barking,—thus one bark was for one, two barks for two, etc. Every correct solution was rewarded with a piece of cake. Huggins states explicitly that he gave no signals voluntarily, but that he was convinced that the dog could see from the questioner's face, when he must cease barking, for he would never for an instant divert his gaze during the process. Huggins was unable, however, to discover the nature of the effective signs. This satisfactory, though still unproven, explanation has been accepted by specialists, among them Sir John Lubbock.[60] I, too, regard this dog as a predecessor of our Hans.
A similar case is reported by Mr. Hugo Kretschmer, a writer of Breslau, in the "Schlesische Zeitung" of August 21, 1904. To him I am beholden for a detailed written statement, which he has kindly permitted me to use in this connection. The gentleman named, first trained his dog to ring the table-bell, and this, by pressing the dog's paw upon the bell-button. When the dog had learned to do this independently, his master tried to teach him the rudiments of numbers, in such a way that the animal was to give one ring of the bell for the number 1, two for 2, etc. But these attempts failed utterly and had to be abandoned. But Mr. Kretschmer had noticed that he was able to get the dog to ring any number which he, Mr. Kretchmer, might decide upon. (Success was always rewarded by a bit of bread and butter.) At first Mr. Kretschmer tried to imagine vividly only the final number, but failed thereby to elicit correct responses from the dog. But he did succeed when he tried making a series of separate volitions. Thus for the number 5, he would "will" each separate push of the button on the part of the dog. Even so, however, he never got beyond 9, for then the dog would become impatient and would ring the bell continuously. Anything that diverted the dog's attention, such as noises, etc., also entailed failure. In these tests master and dog had faced each other, each gazing steadfastly at the other. Mr. Kretchmer was convinced, however, that the dog was not guided by any sort of sign, but rather by suggestion. He based his belief on the following two observations. After some practice, he says, the tests were also successful when he did not look at the dog, but stood back to back with it, or when he screened himself from the dog's view by stepping to one side behind a curtain. The tests were unsuccessful, on the other hand, whenever he was mentally fatigued or had taken some alcoholic drink. The arguments do not appear to me to be adequate. If he turned his back upon the dog and no other observer was present, he had no means of knowing whether the dog did not, after all, peer around to get a peep at him. If others who knew the desired number, were present, the dog might have gotten his cues from them. And there may be some doubt whether the curtain adequately served the purpose for which it was intended. At any rate, it was added that all attempts to influence the dog from an adjoining room—which would thus exclude effectively all visual signs—were utter failures. I am also strengthened rather than weakened in my belief, by the second argument which Mr. Kretschmer makes, viz.: that mental fatigue or the use of alcohol on the part of the questioner tends to make the result unsatisfactory. We noted a similar effect in the case of the horse ([page 150]), where a disturbance of the "rapport" between the questioner and the horse was invoked by some by way of
explanation. The facts were explained by us much more simply. We attributed the result to the close correlation between the type of mental concentration and the nature of the expressive movements—a correlation which we have shown experimentally to exist. I cannot, therefore, subscribe to the view that this dog did not require either visual or other sensory signs. The tests which were made for the purpose of strengthening that view, are on a par, I believe, with those mentioned on [page 45]. And since auditory, olfactory, and other stimuli, though not impossible, still are improbable, I believe that our Hans, Huggins's dog, and the one belonging to Mr. Kretschmer, differ from one another only in this, that the first taps, the second barks, and the third presses a bell-button.
And finally I have access to a letter from the Rhine Province in which there is a brief account of a dog that would promptly obey any command that was given without a sound and supposedly without the accompaniment of the slightest kind of gesture. It is specially mentioned that the animal steadily watched its master during these tests. The perception of the slightest involuntary expressive movements is in all probability the secret in this case also. Here, too, suggestion has been invoked by way of explanation, but there was not the slightest attempt made to find for it a more specific foundation, and we cannot suppress an objection based on the matter of principle. It is incumbent upon anyone who uses a term so ambiguous, to define what content he desires to have put into it. If he does not do this, he is giving us, instead of a concept, a bare word, instead of bread, a stone.
While we must reject the explanation based on suggestion,[AC] we believe, on the other hand, that we have here again, evidence of the presence of visual signs, given unwittingly and involuntarily, just as I am sure that they were involved in the two preceding cases, and similarly in the case of the Huggins dog. Since the effective signs were discoverable in none of these canine predecessors of Hans, an investigation would be desirable, based upon the insight gained as a result of these experiments upon Mr. von Osten's horse. Unfortunately this is impossible, since the dogs in question are dead. But others like them undoubtedly exist in many places. We might mention that when Hans first came under the limelight of public attention, there was also frequent reference to the Huggins dog, but he soon dropped out of the discussion again.[63] And this for two reasons. The dog never took his gaze from his master and appeared to be entirely dependent upon him in his reactions. Hans, on the other hand, seemed to give evidence of a high degree of independence and never appeared to look at the questioner. But we know now that, though he was never dependent upon the will of his master, he, too, abjectly hung upon the man's involuntary movements and never for a moment lost him from view. But since the horse is able to observe with one eye alone, and needed to direct only it and not the entire head toward the questioner, in order to focus comfortably, one could not conclude as to his line of vision from the direction of the head. Since, furthermore, in the horse the pupil is hardly distinguishable from the darkly pigmented iris and since the white sclerotic is hidden by the eyelids, except when the eye is turned very much, it is difficult to determine what direction the eye is taking. I once purposely stepped backward to the horse's flank, so that he had to turn his eye far back and thus the outer border of the iris and the white sclerotic coat became visible and all doubt concerning the line of vision was removed. This doubt could never arise in the case of the dog, the median plane of whose head is always directed toward the object fixated, and Zborzill is justified in saying, as he does, in his discussion of training of the kind mentioned on [page 177], "But any careful observer can immediately guess the manner in which such a dog has been trained."[64] If Hans had chanced to possess so-called "glass-eyes"—in which the dark pigment is wholly or partly lacking, so that the black pupil is clearly defined against the lighter background,—then no doubt could ever have arisen concerning the direction of the eye, and Hans never would have come to be regarded as the "clever" Hans.
After the publication of the December report, Hans acquired a reputation for excellence in thought-reading and thus the discussion of thought-reading among animals in general became once more the order of the day. That is to say that many of our domestic animals are—like the human mind-reader (à la Cumberland),—supposed to have the ability to infer the thoughts of their masters from slight, involuntary movements. They are thus aware when the feeding hour approaches, when they may go out in the open, etc. They also appear to be aware that their welfare lies in our hands, and therefore would seem to have a vital interest in divining our intentions and our wishes. Not only our spoken words, but also numberless movements—usually without our knowing it and often contrary to our desire—speak a clear language. As is well said by the American neuropathologist, Beard,[65] (who first explained the phenomenon of thought-reading, on the basis of the perception of very minute muscular jerks, and therefore called it "muscle-reading" or "body-reading"): "Every horse that is good for anything is a muscle-reader; he reads the mind of his driver through the pressure on the bit,—though not a word of command is uttered." We know that in the case of perfectly trained horses the rider's mere thought of the movement which he expects the horse to make, is seemingly sufficient to cause the animal to execute it.[AD] Such cases are of course very much like that of our Hans, excepting that instead of visual signs they involve aids of a mechanical nature, which, however, does not alter the general principle, since both of them are of the nature of sensory stimulation. But we must not overlook the essential difference between this so-called thought-reading on the part of animals and that which is done by man. The human thought-reader can interpret movements, for he is familiar with the ideas which are their source. Thus when at the second tap, I notice a very slight jerk of the subject's head, and a stronger one at the fifth tap, I infer that he thought of the problem 2+3=5. While the experimenter thus cannot be said to read thoughts, he still infers them. The animal, on the other hand, we may be reasonably sure, draws no such inferences. In its conscious life it remains ever on the sensory level. If we could ask Hans about it, he would probably answer: "As soon as my master stoops forward, I begin to tap; as soon as he moves, I stop. The thing which induces me to act thus is the carrot which is given me; what it is that induces my master to make his movements, I do not know."—It is therefore erroneous to believe that animals require the power of abstract thinking in order to utilize the signs which are consciously or unconsciously given them, as is argued by Goldbeck[68] when he says with reference to the training for visual signs, which we have already mentioned before: "There the dog has consciously interpreted the visual impression in terms of the conclusion that he is expected to bring forth the leaf indicated." Nor was there any justification for the critic who thought he could put the essence of the report of December, given in [Supplement IV], into the following words: "He (Hans) showed that he has the power of attention, can draw logical conclusions, and can communicate the result of his thinking,—and all this independently." Yet none of this had been asserted. The whole thing may be explained satisfactorily by means of a process of simple association established between the signs observed in the master and certain reactions on the part of the horse. The fact that the movements made were so exquisitely minute does not change the matter in the least. Such signs call for a high degree of sensory keenness and great concentration of attention, but by no means an "extremely high intelligence."
Let us turn now from the consideration of visual perception to that of auditory perception in the horse. We saw that the fact that Hans was able to respond to commands which were only inwardly enunciated, that is, commands which were merely thought of but not spoken, was not proof of great acuity of hearing, but rather that hearing was not at all involved. If Hans had been deaf he would, none the less, have promptly obeyed the commands. Blind and near-sighted horses try to overcome their deficiency by means of the sense of hearing, and hence show a pronounced play of ears. In the case of the Osten horse, however, attention has been diverted from auditory stimuli in the process of habituation to visual signs, and as a result ear-movements are almost completely wanting. One is not of course permitted to deny a priori that perhaps some associations might have been formed between objects and the vocal signs belonging to them, e. g., between the colored cloths and the names of the colors if both had been presented together oftener than was the case.