I did not know that yesterday!

How does the nozzle on the fuel pump know when to shut off to avoid
overfilling the vehicle?

As How Things Work from the University of Virginia explains, gasoline nozzles have a small hole at the end that becomes blocked when gasoline rises to the top of the tank. Once this happens, the pressure drops inside a valve system built into the pump. This cuts off the gas flow. If you want the nitty-gritty details, check out The Straight Dope. And if you don't believe me, check the end of the gas pump the next time you're at the station. You should be able to see the valve system hole.

I also found a suggestion from Dr. Ezra of Cornell University. He states the valve system is sensitive to air pressure within the tank, which increases as the tank fills with gas. Dr. Ezra, I respect your diploma, but this is simply not true.

And as to the rumors that cell phones can start gas station fires, Engadget tells us that it just ain't so. Sadly, this hasn't stopped a Connecticut state senator from trying to introduce a bill requiring drivers to hang up their cell phones before filling their tank. Yeesh.