Ads at the side of the threads

[dancecaller]

I am fascinated by the way adverts are linked to topics in threads, but are they also linked to the reader, like my cookie?

I just saw one for a firm that had my home county in the ad title.

Mind you they often get the slant of the advert completely at odds with the posts. In the animals and nature section you can see lots of ads for ways of killing things.