Koko, the signing gorilla, would sometimes get bored answering questions. She’d often give incorrect answers to indicate impatience. But sometimes, she was just messing with the researchers.
One day she was being shown a series of towels and asked the color. At one point the researcher held up a red towel and asked the color, and Koko signed “blue.” After correcting her the tester asked a gain, and again she signed “blue.” When she kept giving the same answer, the researcher expressed impatience, and began to put away the towels and continued to indicate the color as red.
Koko leaned in and plucked a single blue thread that had been clinging to the red towel. She held it right up to the tester’s face, signed “blue,” and folded her arms to indicate that she was done for the day.
Once, left alone for a few minutes, she tore a sink off the wall. When asked who had done it she signed “All Ball,” which was the name she had given her pet cat.
I’ve recounted these stories from memories of articles I read years ago. Some details, such as the actual colors referenced, may have been different in the actual case.
Second, there are some in the animal behavior research community who say that Koko actually signed gibberish most of the time and that the “hits” she made were really a matter of selection bias by the researchers.