To the extent that animals like Kakama, Kanzi, Viki, and Koko can pretend, their imaginations are probably limited in the same way as young human children. They can imagine, though they might not have a complete awareness of the distinctions between reality and fantasy. They might pretend, but not recognize it as such. Decades of intensive observation have revealed that under some circumstances, animals can imagine the future or the past, can pay attention to imaginary objects, and can pretend that one object is another. In some extraordinary circumstances, non-human animals have been known to feign interest or emotion, a type of pretence, in order to distract a rival from food or a mate.
One type of make-believe that has never been observed in an animal, though, is the sustained relationship with an imaginary other. To the best of our knowledge, no animal has an invisible friend. Still, the likes of Kakama, Kanzi, Viki, and Koko show that even imagination, something that Carl Sagan wrote could "carry us to worlds that never were," is far from uniquely human.