Orange-trees line your way almost wherever you go - but do not even think about picking any of the oranges, because if you do, you will get a nasty surprise. They are for decoration only, not for eating, and these wild naratsias are actually inedible. And there is something else to watch out for, too, the policeman who happily let you drive around to your heart's content yesterday might not seem in quite such a good mood about it today. But, relax, you have not done anything wrong, it is just Athenian traffic policy. Vehicle pollution is always a problem, and to try and reduce it the authorities have come up with a scheme to allow cars with even numbered plates into the centre one day and cars with odd numbered plates the next.