Adsense check with every ad view?

Hi,

just noticed inside the logs that Google Adsense visits a site with every page view:

66.249.66.237 - - [14/May/2007:08:36:28 +0200] "GET /video_tags.php?page=4&tag=wii HTTP/1.1" 200 13981 "-" "Mediapartners-Google/2.1"

I think they do that to check if a possible click is done by human.

the bad thing is that every page view costs double bandwidth (of course only the html)

Edit: The strange thing is that they visit the site 2 or 3 seconds later...maybe its only because the page is viewed the first time, what do you think?

they spider each time to determine what ad to show in your page...

looks to me only once in a while

I've noticed the same thing and assumed it was to determine which ads to show, like Vince said.

That's right. Whenever a new page visited, the bot is crawling it to determine the content.

I think this is also relative to the headers you sent. For a dynamic page the bot will visit more often.