Final answer:
Washoe displayed the linguistic capacity of combining units in an infinite number of ways to produce new meanings by inventing words like "water-bird" and "feces monkey." This capacity is a unique attribute of human language.
Step-by-step explanation:
In inventing words such as "water-bird" and "feces monkey," Washoe displayed the linguistic capacity for combining units in an infinite number of ways to produce new meanings. This ability is a distinctive biological attribute of human language. Unlike animal communication, which is limited to specific contexts, human language is open-ended and allows for the invention of new words and the creation of new meanings.