We shouldn't forget, if you get 600,000,000 results for the keyworld "girl", it doesn't mean that 600,000,000 surfers searched for "girl". It only means there are 600,000,000 sites related to the topic "girl".
The number of people who are searching for "girl" is in fact much smaller. Perhaps just a few thousand per month.
If you like and didn't know the link yet, check the google archive of popular search queries in countries around the world.
Google Press Center: Zeitgeist Archive
Here the March 2008 archive
Google Press Center: Zeitgeist Archive
It's amazing what people are looking for. And words like "girl" or "sex" or similar terms aren't in the topranks at all.