Chest-slapping can be a silly gesture for gorillas.
Ndume (Koko’s male companion) enjoys taking afternoon naps in the sun in a nest of blankets. When he’s not napping and feels particularly happy, he often plays with his blankets and other enrichment items. In this video Ndume has fun with one of his favorite pieces of enrichment and makes a series of gestures, including: sweep-foot, pat-foot, pat-shoulder (which is the sign for Koko), hair and chest-slap. Chest slapping for gorillas can be used to communicate a variety of things. In this case Ndume uses a playful “blind” chest-slap to let us know that he’s having a good time. Notice how Ndume seems to return to a meditative pose at the end.