A Very Clever URL Joke
I was randomly browsing XKCD the other day, and saw something funny. If you go to http://xkcd.com/405/ and click on the Previous button, you're taken to http://xkcd.com/403/. If you click Next from there you're taken back to http://xkcd.com/405/. If you click Previous a bunch, you'll see that you're taken to 402, 401, 400, 399, 398, etc. And vice versa for clicking on Next.
See anything strange?
(Answer) :)