Another one like that is the hot potato that everyone is interested in. Someone says something difficult or controversial, and everyone seems to want to say something, but they don't want to get into an escalating conflict. So the post sits for a long time, and then gets its first reply. After that, the exchange builds slowly but pretty soon everyone wants to give their opinion. Those are very often the kind that turn into 100-post threads.

Sometimes the group dynamic is as interesting as the discussion.