Counting katydid

Harvard physicist George W. Pierce studied insects:

There was a katydid in Dr. Pierce's laboratory that learned to count and thereby alter its usual two-beat rhythm. During an experiment, a laboratory assistant who could imitate the katydid's shrill "zeep-zeep," made the sound in three beats instead of two. The katydid answered with three beats. The assistant then tried four, and the katydid answered with four. Then the assistant tried five and the katydid answered with five. At the next stage, however, the insect lost count and, on its own, began to improvise on the numbers it had already learned.

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