In 1972, Dr. Francine Patterson started to teach sign language to Koko.

Dr. Patterson: She made the sign for cat.

Koko knows and uses more than 500 words in sign language, the language of deaf people.

Dr. Patterson communicated with a gorilla using sign language.

Deaf people can talk in sign language.

Dr. Patterson: Not at all! Koko has taught us that gorillas are intelligent enough to learn sign language.