A fair part of it seems to be simply terminology ("When we play like this, we call that a fnurgle."). That makes sense to me, mostly. The thing that boggled me the hardest today was the fact that if you end a melody on the same note you started it, that's heard as a satisfactory ending. End one note higher and it just sounds wrong. This is, apparently, an effect that's embedded in the brain's hearing firmware. And that's just weird.