It goes without saying that a smile is the universal welcome, and at the heart of manners and courtesy all around the world.
The trouble is that we are all different, and one man's smile could turn out to be another man's grimace.
I once knew a man who had a perpetual hangdog expression, and when he smiled it looked like a sneer. This led to all kinds of trouble, especially in pubs, where he was arrested for inadvertently causing violent fights on several occasions. All the worse as he was vicar. A woman friend has a nervous tic which causes her sometimes to giggle with a clucking sound when she smiles. This caused great embarrassment when she was introduced to a member of the Royal family visiting her place of work.
The visiting duchess's customary pleasantry was greeted by a forced smile and convulsive clucking noises. The situation was only saved by an equerry who stepped in and directed the royal gaze out of a nearby window to an fascinating skip full of building debris.
Some people are by nature wild-eyed. This twinkle can project both fun and passion but if it is coupled with a slightly twisted smile, may give the appearance of being a psychopathic killer. Such people must be very careful with their smiles and above all never raise their right arm in what could be construed as a repetitive stabbing action.
The shadow of our smiles may colour people's dreams - but they may also tint our nightmares. There is little we can do about "real" smiles, but if we have to make forced and formal ones it is a good idea to check them out in the mirror and test them on a friend.
