A 3-year-old Koko is in the kitchen of her trailer at the San Francisco Zoo. First, Penny gives Koko a pink wool hat, and she promptly rejects it as “stupid.” Then Koko puts on the hat and pulls it down over her eyes, blocking her vision. Koko parades around the counter with a giant grin on her face. Koko was always a little bit mischievous. So, planning cognitive studies with Koko required taking into account her mischievous streak and keeping activities fun and engaging. You can readily see Koko’s sense of fun here.
Encouraging Koko to express herself allowed us to discover more about her unique personality, and more generally about the inner nature of gorillas as a species.