For the second series, given on May 4, the conditions were unfavorable
in that it was dark and rainy, and the noise of the rain on the roof
frightened Sobke. He refused to work after the fourth trial, and the
series had to be completed on the following day. The total time required
for this series was seventy-eight minutes.

The work on May 6 was distinctly better, and the animal's behavior
indicated, in a number of trials, definite recognition of the right
door. He might, for example, make a number of incorrect choices, then
pause for a few seconds to look steadily at the doors, and having
apparently found some cue, run directly to the right box. No aid from
the experimenter was needed in this series.

On the following day improvement continued and the animal's method of
choosing became definite and fairly precise. He was deliberate, quiet,
and extremely business-like. The time for the series was thirty-one
minutes.

The period of punishment was increased on May 12 to thirty seconds.
Previously, for the greater number of the trials, it had been ten to
fifteen seconds. This increase apparently did not disturb the monkey,
for he continued to work perfectly throughout the series, although
making many mistakes in spite of deliberate choices and the refusal of
certain boxes in each trial.

An interesting and significant incident occurred on May 13 when at the
conclusion of trial 5, Doctor Hamilton came into the experiment room for
a few minutes. Sobke immediately stopped working, and he could not be
induced to make any choices until Doctor Hamilton had left the room.
This well indicates his sensitiveness to his surroundings, and his