Koko the gorilla, famous for her ability communicate with her keepers using American Sign Language, has also developed breathing and grunting patterns associated with the ability to talk – something scientists thought to be impossible in her species.

Postdoctoral researcher Marcus Perlman at the University of Wisconsin-Madison and Nathaniel Clark at the University of California studied 71 hours of video footage of Koko interacting with her keepers and identified vocalizations thought to be impossible for gorillas.

The researchers say that they have “found examples of Koko performing nine different, voluntary behaviors that required control over her vocalization and breathing.” The 44-year-old ape’s sign-language training began in 1972, and she has spent most of her life working with humans.