Google Breadcrumbs come from … Breadcrumbs

Google sometimes shows breadcrumbs in their search results.
Instead of showing the URL of the page you’re going to visit (in the green bit), hey’ll show a path kind of like so:
Homepage › Category › Subcategory > Something something.
Many SEO experts have been trying to figure out just where they come from. So have I.
So recently, on one of my websites: promoties.be. I had the chance to figure it out.

All promotions are divided into categories and subcategories. The URL of these categories are always hierarchically mapped.
e.g. http://www.promoties.be/categorie/autos-motoren-27/aanhangwagens-1419 is a subcategory of http://www.promoties.be/categorie/autos-motoren-27 making the URL logically traversable.
However a specific offer or product under this category is not in this structure. Mainly because that would make the URL way too long.
An example is http://www.promoties.be/promotie-bw1-aanhangwagen-864809. As you can see, the categories do not appear in the URL.

However the breadcrumb for this offer is as follows: Home > Promoties > Auto’s & Motoren > Aanhangwagens > Bw1 aanhangwagen with all the nested categories intact.

Now the Google search result block for this specific offer was the following:

Google search result for "Bw1 aanhangwagen"

In this case we can conclude that Google took the breadcrumbs in the search results, from the breadcrumbs on the page.

More info on breadcrumbs:

http://www.google.com/support/webmasters/bin/answer.py?answer=185417