Watch the Hands
You put out your hand. Petra leans in to kiss your cheek. You both stop, half a metre apart, and laugh.
This happens to visitors everywhere, because a greeting is a small tradition, and traditions are local.
In most of Japan, people bow. The bow is short, and nobody touches.
In France, friends kiss on the cheek: two kisses in Paris, but three or four in some other places. There's a lot of variety inside one country, and French people ask each other about it too.
In Thailand, you put your hands together in front of your chest. It looks calm, and it's easy to copy.
In Germany, a handshake is short and firm. In some offices everybody shakes hands with everybody, and it takes a while.
So which one is the right one? All of them. The traditional greeting is the one the other person is expecting.
For a visitor, that view makes the rule simple. Watch the other person's hands for one second. Then do the same thing.
Aiden got it wrong in Paris and right in Bangkok, and he says the second one felt much better.
