Brâncuși spent something like twenty years chasing this exact shape — no feathers, no wings, not even a head, because from what I've read he wasn't after what a bird looks like, just the feeling of one lifting off. He's said to have carved or cast this same idea more than a dozen times, in marble and in bronze. One of the bronze versions ended up in a legal fight when US customs refused to wave it through as art and taxed it as scrap metal instead — the case that followed is apparently still taught as the moment the law had to decide what actually counts as sculpture.