I've never done this before. Hope the parties involved are not embarrassed by being pointed out. I feel strongly about clarity of thought and writing in Astrophysics and Cosmology. Every once and a while I see a brief exchange that is exceptionally well written from both sides. Someone asks a thoughtful question very clearly and someone else answers it very accurately and clearly. No words wasted and no confusing loose ends. Nice. Can anybody beat this, as an exemplary Q/A exchange for this month of April 2013? It is a really good question. Why doesn't darkmatter clump? If you see another highquality efficient exchange like this during April in Astrophysics or Cosmology, I hope you will add it to this thread, as a kind of Kudo list. We'll see how good we are as a group, at asking and answering this sort of questions.