Washoe the chimpanzee was angry with her caretaker, Kat. Kat hadn't visited her in a very long time and that just wasn't okay at all. When Kat returned, she explained to Washoe that she was gone because she lost her baby.
Then, Washo did something amazing. She signed her grief. She even made the sign for "cry," as chimpanzees aren't actually able to physically cry. What came next was unexpected.