Babies sometimes laugh and sometimes cry. It doesn't take a genius to decode the meaning of these sounds. But it isn't quite as straightforward to decide the meaning, if any, of an infant's babbles. And humans a little older can make the same sounds regardless of how you actually feel—you're able to say "I'm hungry" whether you're ravenous or just gorged yourself. Scientists think that the ability to make the same sounds across a range of emotional states is critical to language development. They also believe it to be uniquely human, because in previous studies of animal communication, researchers only observed fixed vocalizations. For example, bonobo chimpanzee pant-laughs and threat barks are tied to a specific emotion or behavior. But the new study finds evidence that bonobos in the wild are also capable of flexible vocalizations.