Actually their real 404 page, e.g. http://notfound.org/something.html http://notfound.org/something.html or http://notfound.org/404 http://notfound.org/404 or h

Actually their real 404 page, e.g. http://notfound.org/something.html http://notfound.org/something.html or http://notfound.org/404 http://notfound.org/404 or http://notfound.org/bla.xml http://notfound.org/bla.xml do display children. What you happened to stumble upon was an existing page called 404.html, which of course is a bit funny.