Koko is one of the few non-humans known to keep pets of a different species. She has cared for several cats over the years and Koko's relationship with All Ball was featured in the 1987 book Koko's Kitten, which was written by Patterson.
"Koko: A Talking Gorilla" is a 1978 documentary directed by Barbet Schroeder that focuses on Dr. Francine 'Penny' Patterson and her work with Koko, the gorilla Patterson claims to have taught to communicate with humans using symbols taken from American Sign Language.
i found the documentary on youtube. below is part 1/9 (it's in english with italian subtitles):