See Tom Clark's blog ("Beyond the Pale") for a speculatiove answer, from which an excerpt appears below:
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During this time, subject develops a terrific degree of sensitivity to acoustic and optical stimuli. At the same time, criticism is expressed that the experimental conditions are unfavorable. Such an experiment ought to be successful in a palm grove. Otherwise, the dosage he received was said to be too negligible for B[enjamin]: a train of thought that surfaces again and again throughout the course of the experiment, and which eventually allowed irascible indignation to become expressed.
During this time, subject develops a terrific degree of sensitivity to acoustic and optical stimuli. At the same time, criticism is expressed that the experimental conditions are unfavorable. Such an experiment ought to be successful in a palm grove. Otherwise, the dosage he received was said to be too negligible for B[enjamin]: a train of thought that surfaces again and again throughout the course of the experiment, and which eventually allowed irascible indignation to become expressed.
In the course of checking his pulse, B[enjamin] reveals
himself to be terrifically sensitive to the slightest touch. (Pulse itself
unchanged.) In the course of the discussion about sensitivity, the phenomenon
of tickling acquires a powerful significance. Attempt to explain tickling
as approaching a person a thousandfold, laughter as defense
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