Koko is a 35 year old gorila who uses human sign language. Koko was taught sign language by psychologist Panny 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 more, and eventually learned abstract ideas such as love, jealous, and shame. It is believed that Koko can sign over 1000 words, and that she understands about 2000 spoken words. Koko is also famous for having had pet kittens. She has always been extremely gentle and affectionate with her kittens.