If a HTTP request triggers an unexpected response it is interesting to see if it’ll trigger a response if it follows a “good” request in the same Keep-Alive connection. It’s non-trivial to define a “good” request: http://censored.org/robots.txt may still be filtered because of the domain and webserver MAY drop connection after the /robots.txt request to the domain that is not served, but Apache and Chrome are okay with the trick.
This is related to tq-018 Request to dummy proxy.