Koko is a 35-year-old gorilla who uses humen sign language. Koko was taught sign language by psychologist Penny Patterson when Koko was just a baby. Patterson had been studying whether gorillas could be taught to communicate. Although the study was only supposed to last a couple of years, Patterson and Koko developed a lifelong bond and have been working together ever since. Koko began by learning basic words like eat, drink, and eventually learned abstract ideas such as love,jealous,and shame. It is believed taht Koko can sing over 1,000 words,and that she understands about 2,000 spoken words. Koko is also famous for having had pet kittens. She has always been extremely gentle and affectionate with her kittens.