Gorillas, like humans, are able to vocalize whenever they feel like it.
In this video Koko has just blown a kiss to a caregiver job applicant who was leaving he premises, as Penny enters and asks Koko to demonstrate some of her other pre-fabricated vocalizations. In particular, Penny asks Koko to do her “fake sneeze,” which she easily accommodates. Some researchers claim that great apes have no control over their vocalizations, that they are involuntary. Koko certainly disproves this hypothesis, as you can see in this and and a number of other KokoFlix video clips (more to be added soon).