From Freedom to Tinker:
You probably know already that the Chinese government censors Internet traffic. But you might not have known that you can experience this censorship yourself. Here's how:
(1) Open up another browser window or tab, so you can browse without losing this page.
(2) In the other window, browse to baidu.com. This is a search engine located in China.
(3) Search for an innocuous term such as "freedom to tinker". You'll see a list of search results, sent back by Baidu's servers in China.
(4) Now return to the main page of baidu.com, and search for "Falun Gong". [Falun Gong is a dissident religious group that is banned in China.]
(5) At this point your browser will report an error -- it might say that the connection was interrupted or that the page could not be loaded. What really happened is that the Great Firewall of China saw your Internet packets, containing the forbidden term "Falun Gong", and responded by disrupting your connection to Baidu.
(6) Now try to go back to the Baidu home page. You'll find that this connection is disrupted too. Just a minute ago, you could visit the Baidu page with no trouble, but now you're blocked. The Great Firewall is now cutting you off from Baidu, because you searched for Falun Gong.
(7) After a few minutes, you'll be allowed to connect to Baidu again, and you can do more experiments.