Another time, a caregiver showed the ten-year-old Koko a photo of a bird in a magazine. THAT ME, Koko signed. "Is that really you?" KOKO GOOD BIRD, she responded. "I thought you were a gorilla." KOKO BIRD. The caregiver asked, "you sure?" Koko responded, pointing to the bird, KOKO GOOD THAT. "Okay, I must be a gorilla," the caregiver said. BIRD YOU, the gorilla signed. "We're both birds?" Koko responded by signing GOOD. "Show me," the caregiver prodded. FAKE BIRD CLOWN. "You're teasing me. What are you really?" Finally, Koko gave in, with a laugh: GORILLA KOKO.
By pretending to be a bird, Koko is doing something that the youngest human infants can't do. Young infants attempt to grasp objects in pictures as if they're really there. But by nineteen months, on average, grasping is replaced by pointing. By that age, human infants begin to understand that a picture is a representation of another object, not the object itself, much the same as a ten-year-old Koko understood that she wasn't truly a bird.
On the other hand, children under four years seem able to pretend in some instances but not in others. For instance, three-year-old children routinely agree that a balloon on a television screen would float to the ceiling if the top of the set was removed.
Koko, too, in some instances couldn’t distinguish between pretence and reality. In one interaction, a caregiver brought a toy dinosaur and hid it between her legs as she sat with the eleven-year-old ape. The caregiver poked the toy dinosaur out from behind her legs, causing Koko to jump backwards. "I scared you!" said the caregiver, "what's this?" Koko answered FAKETOOTH FAKE. "Yes, it's a fake alligator." Dinosaurs, lizards and alligators are all labelled "alligator" in Koko's vocabulary. After playing with the toy for a while, the caregiver asked, "You like it? You want it?" Koko responded GOOD, but still she didn't take it. The caregiver pretended as if the toy bit her own finger, shouting "Ow!" as if in pain. TOILET STINK, Koko replied. "Give me your finger, Koko," the caregiver instructs. But Koko instead offered a toy doll, letting it get bitten instead. "You funny Koko, let monster bite doll instead of you. Let's try being nice to it. It's a nice animal." The caregiver kissed the doll, to which Koko responded with the sign FAKETOOTH. "You want to kiss it, be nice?" While Koko eventually, though cautiously, kissed the dinosaur, she quickly withdrew.
Koko seemed aware that the dinosaur was only a toy, using the signs FAKE and FAKETOOTH, both of which she regularly used to indicate that objects aren't real. However, she was also scared of it, acting quite wary about touching or kissing it. On some level, perhaps, she thought that the toy dinosaur could actually harm her.
Like a human child under four years of age, it might be that Koko didn't understand the concept of pretending, or didn't apply her knowledge of pretence uniformly. Despite the fact that she knew and understood the sign for "pretend", Koko more often used the signs for "know" and "think" when asked about her toys.
That said, one does not have to be aware that they are pretending in order to successfully pretend. In one clever study, researchers asked human children if a troll that hopped like a rabbit was only pretending to be a rabbit, even if he had never heard of rabbits in the first place. It wasn't until children were at least four years old that they answered correctly, suggesting that the younger children did not yet understand that pretending was something associated with the mind rather than the body.