Comment by AnimalMuppet

Gas isn't a continuous medium, either; it's made up of particles. (Not even true particles, either, and sometimes that matters.) We can still create equations for sound waves, though.

Now, sure, humans are more complicated than gas molecules, and have an element of choice in what they do. But in bulk, they still behave in ways that can be modeled mathematically - perhaps not perfectly, but enough that it can still give some actual insight.