This is Washoe, the first non-human to use sign language. When her caretaker Kat suffered a miscarriage, and Washoe was told that her baby had died, she signed "CRY", drawing a path down her cheek with her finger to mimic a tear. Chimpanzees don't shed tears, and Kat said this one sign told her more about Washoe's mental capabilities than all of her longer, grammatically perfect sentences.

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