The Japanese smile takes its cue from the days when Samurai women were required, like the women of Sparta, to express joy on hearing that their men had perished in battle. To betray any sign of sorrow was a serious breach of their code of honor. In many lands, Sri Lanka, India, the Gulf States, and many nations in North Africa, smiling at a member of the opposite sex is taken as an invitation to flirt or have sex. In 1992 millions of workers and senior management in Eastern Europe were trained in the ways of the West. One part of the training suggested smiling while they were on the telephone.
People can hear the difference.
Not all smiles are warm. Actors and actresses know that on stage smiles need to be exaggerated, even if the recipient's face is only inches away, before the audience in the back row can see it. The skillful actors recognize faked smiles must also include smiling eyes if they want to be convincing. As we grow older, we smile and laugh less. With friends around us smiling less, we tend to fall into the same social behavior.