"a bird's tool is its own body, that is, its breast, with which it presses and tightens its materials until they have become absolutely pliant, well-blended and adapted to the general plan.” Michelet suggests a house built by and for the body, taking form from the inside, like a shell, in an intimacy that works physically. The form of the nest is commanded by the inside. "On the inside," he continues, "the instrument that prescribes a circular form for the nest is nothing else but the body of the bird. It is by constantly turning round and round and pressing back the walls on every side, that it succeeds in forming this circle." The female, like a living tower, hollows out the house, while the male brings back from the outside all kinds of materials, sturdy twigs and other bits. By exercising an active pressure, the female makes this into a felt-like padding.
Michelet goes on: "The house is a bird's very person; it is its form and its most immediate effort, I shall even say, its suffering. The result is only obtained by constantly repeated pressure of the breast. There is not one of these blades of grass that, in order to make it curve and hold the curve, has not been pressed on countless times by the bird's breast, its heart, surely with difficulty in breathing, perhaps even, with palpitations." (Bachelard, The Poetics of Space, pg. 101)