snaps shut and stops you from filling the car. Called a misfuel device.
Fitted to thousands of cars as an OE thing these days.
My car has one.
Still doesn’t stop some idiots physically hammering the wrong nozzle past the device to fill with the wrong fuel.
Much like those we get putting diesel in a petrol. By using good aim and spraying diesel down the side of their car (or physically hammering the wrong nozzle into the filler head.)
Doesn’t work so well in countries where they play fast and loose with what nozzle they actually put on the gun though. Or some of the low cost chains who also don’t really care.