Although not unique Koko is one of the few non-humans known to keep pets. Researchers at the Gorilla Foundation said that Koko asked for a cat for Christmas in 1983. Ron Cohn, a biologist with the foundation, explained to the Los Angeles Times that when she was given a life-like stuffed animal, she was less than satisfied. She didn’t play with it and continued to sign “sad”. So on her birthday in July 1984, she was able to choose a kitten from a litter. Koko selected a gray male Manx from a litter of abandoned kittens and named him “All Ball”. Doctor Penny Patterson, who had custody of Koko and organized the Gorilla Foundation, wrote that Koko cared for the kitten as if it were a baby gorilla. Researchers said that she tried to nurse All Ball and was very gentle and loving. They believed the kitten, and her skills gained through playing with dolls, would be a tool to help Koko learn how to nurture an offspring.
In December of that same year, All Ball escaped from Koko’s cage and was hit and killed by a car. Later, Patterson said that when she signed to Koko that All Ball had gone, Koko signed “Bad, sad, bad” and “Frown, cry, frown, sad”. Patterson also reported later hearing Koko making a sound similar to human weeping.
The Gorilla Foundation also briefly played home to a male green-winged macaw of mysterious origin who had been found inhabiting the grounds and feeding on the loquat trees, though he was not a pet of Koko’s in the same way her cats were. Initially frightened of the parrot, Koko named him “Devil Tooth”, “devil” presumably coming from his being mostly red, and “tooth” for his fierce-looking white beak; the human staff adjusted the name to “Devil Beak”, and ultimately to “DB”