Coiled Aster petals

Not a great photo, but I wondered if anyone has any suggestions as to why the petals on one of the flowers are all so precisely coiled! I've never seen this before. Note on 13th September 2007: I have just been looking at a photo and information about the New England Aster (on Google), and it said that "once pollination has finished, the rays of the bloom begin to turn brown and curl up like a party whistle." In the photo I found, some of the petal coils were still purple, like mine. So, mystery solved!