I've just finished watching a documentary in which Nitin Sawhney composed a symphony for animals to listen to. It was successful for starlings, a parakeet, and a seal; dogs and wolves seemed nonplussed. Believe it or not this is actually a burgeoning field of study; it turns out all kinds of animals can and will respond to musical cues. Some of what is going on seems to concern teaching animals how to interact with music; some of it concerns finding out what kind of music animals naturally respond to.
I think there is something very moving about the former, but I find the latter more interesting. It turns out that we can figure out what kind of music monkeys like and compose it for them. (There is something Bartok-esque about it - I actually kind of enjoy it for that reason.) There are even people making music for cats (think Brian Eno doing something ambient).
Naturally enough, thinking about all of this my mind starts to wander: what if people in a fantasy world knew how to make music for dwarves or goblins or dragons?
Let's take that further. Imagine it was impossible to communicate through language with other races: humans, dwarves, elves and so on simply lack common key concepts which make true communication possible. But what if music - rhythm, tone, pitch - was something that all living things understood? You might not be able to really talk to a dwarf. But maybe through music you could find a way to share certain messages, emotions and so forth.
In this world, bards are essentially translators. The local dwarf citadel and human kingdom have been at war. As a peace overture, the humans send a bard to play certain melodies which communicate good faith and sincere intentions. Meanwhile a nearby orc tribe is gathering its warriors to take advantage of the human kingdom's weakness. A bard is sent with a group of drummers to beat out a rhythm from a mountaintop which will tell the orcs, "We're ready." The bard PC is like a snake charmer who gradually learns more and more specific ways to communicate with monsters and animals through music - and can improvise at a push.