Spamtraps are webapplications trying to flood spammers e-mail databases whith useless information. They try to "feed" and "trap" e-mail harvesters by generating pages filled with invalid e-mail addresses and links pointing to the spamtrap itself. If the harvester follows these links it collects more and more useless address and so the spammers database will be filled with junk.
It is a widely used way to expose spamtraps to simply refresh the pages and compare the results. Most spamtraps generate random HTML code by every download, so if the versions differ we can guess that we have found a trap. Spamtraps can be blacklisted too.