Gorillas have a mind of their own, and can be as creative (and endearing) as humans when playing. However, they're not perfect.
Penny asks Koko to do something imaginative with a yellow balloon. Koko compares it to her yellow-dyed tongue (the result of sucking on a non-toxic yellow marker earlier that day), then does some juggling with the balloon and finally pretends it is a baby (at Penny’s request). Koko is clear about how to treat a baby — gently, and with love and playfulness.
Later that day, Koko decides to sketch on the ballon with a black pen, adding strands of “hair” to a gorilla face. She seems quite pleased with her work and signs “good” and blows kisses to let Penny and Ron know she approves and is one happy gorilla.