Well mostly just a song which plays while you go through the text level. We've got a long, long way to go to get sound for everything, but this isn't half bad.
There isn't really a screen shot for this, so you'll have to take my word on it.
Anyway, all the songs are going to be in the format known as "ogg". This means you should be able to replace any of them with songs you like.
It turns out the entire development team is composed of sub par musicians, so we will never make you listen to what you don't want to.
Regardless, when it comes out, you might as well just go ahead and replace the songs with something like this: