repetition

In bird song, the interesting thing is that the bird repeats the same pattern, but not exactly. Within that apparent set of rules, that apparent shape, there is always a tiny freedom that is always improvised and that is not, in computer terms, an exact repetition. From a distant perspective, it may seem like an automatic repetition, but in fact, close by, no two phrases are the same. And I imagine that if you got close enough, you would come to the point where there's no repetition at all.

-- Peter Brook, in "Penetrating the Surface" Parabola 13:2