ect. The errors there were always +1, (whereas
those in the case of procedure with knowledge, which were due to quite
different causes, were very great and inconstant.) The number of +1
errors obtained on this occasion comprises one-fourth of all the plus
errors which were ever obtained in the case of Mr. von Osten during the
entire course of these experiments. Finally, I would mention two
examples of my own. In the course of my very first attempts with Hans I
obtained, as I said on page 89, three responses in a total of five which
exceeded the correct result by 1. This I would explain by the fact that
although I employed a high degree of concentration, I nevertheless was
somewhat skeptical. The result was a certain deficiency in the degree of
concentration. A second example which I would cite is taken from the
period in which I had already discovered the cue to Hans's reactions and
goes to show that I was then still able to eliminate the influence of
this knowledge and to work ingenuously. To the question, "How much is 9
less 1?" I, momentarily indisposed, received the answer 10, and then six
times in succession the answer "9", and finally the correct response,
"8".

Errors of another kind--the not infrequent offenses against the very
elements of counting and the fundamental arithmetical processes--were
regarded in part as intentional jokes and by an authority in pedagogy as
a "sign of independence and stubbornness which might also be called
humor". Hans emphatically asserted that 2+2 was 3 or he would answer
questions given in immediate succession as follows: "How many eyes have
you?"--2. "How many ears?"--2. "How many tails?"--2. These errors, as a
matter of fact, evince neither wit nor humor, but prove incontrovertibly
that Hans had not even mastered the fundamentals.

Many of the errors baffle every charitable attempt at interpretation.
These gave the horse the reputation of capriciousness and unreliability.
If Hans designated the tone "e" as the seventeenth, or "g" as the
eleventh, or when he called Friday the 35th day of the week or believed
50 pfennige to be worth only 48, the cause for these responses lay
either in the insufficient degree of tension on the part of the
questioner (as in the first three examples) or in the extravagant
expenditure of the same (as in the last case). If, therefore, the horse
at times would "hopelessly flounder" which would seem to be indicated by
tapping now with the right and now