essive movements which are normally associated with the
corresponding concepts, this cannot be said to be true of "no" and
"zero". My laboratory observations (see page 107) lead me to conclude
that the movements, by means of which the concepts "no" and "zero" are
naturally expressed, are quite different; and neither of these
corresponds to the signs for "zero" and "no" which the questioner
involuntarily gave to Hans. What was the genesis of these unnatural
forms of expression? If we might assume that the questioner always had
in mind the movement he awaited on the part of the horse, and never
thought of "zero" or "no", then the contradiction would solve itself.
But I must deny decidedly that I ever thought of the movements of the
horse's head, and Mr. Schillings, whom I questioned on this point,
agreed with me in this, in so far as his own mental processes were
concerned. I can see nothing for it but that in this instance the
expressive movements normally connected with the concepts "zero" and
"no" have been replaced by other forms, without the questioner becoming
aware of it. That such displacements may occur, has been shown by the
tests described on pages 107 to 112. That they did occur in this
instance may be concluded from the following observation. In responding
to me, as well as to Mr. Schillings, Hans always moved his head first to
the left, then to the right, never in the opposite order. That this was
_not_ a peculiarity of the horse, but must be ascribed to the signs
which were given him, is shown by the possibility of inverting the order
under experimental control (page 77). Frequently Mr. Schillings and I
had seen the horse respond to his master by means of such
head-movements, and the order was always, without exception, the one
mentioned. It must be assumed therefore that the horse's movement, which
we so often noticed, made such an impression upon us, that afterwards it
was regularly reproduced on our part quite unconsciously, so that Mr.
Schillings never, and I only after a long time, became aware of the
whole process.

In closing, just a word as to the discovery of our own movements. I soon
noticed that every pronounced raising of the head or trunk brought about
an interruption in the horse's response. But only by observing the
final movement in the case of Mr. von Osten did I discover that I, too,
performed a slight erection of the head. Observation of others was less
difficult than the observation of o