I remember when I first learned that adult house cats “meow” almost exclusively to humans and not to other cats. It’s still fascinating to me that in the course of domestication, not only have we selected for certain vocal tendencies in cats but they have also exploited some natural human perceptual tendencies to be able to express what they want – for example, food, affection, or help when they are in trouble. It’s a language, if you will, that exists only between our two species.
Chimpanzees are obviously not domesticated but they certainly are smart, and they have also found unique ways to communicate with humans. The Bronx cheer, or raspberry, is part of the vocal repertoire of many free-living chimpanzees but it is typically used when grooming. Captive chimpanzees, however, have discovered that at full volume it’s a great way to get the attention of humans. And if you do it over and over again, louder and louder each time, the humans will eventually give in. Or go crazy. Either way, it’s enriching for them.