for the other part of the question, many things make me smile such as children's smile, the 'aha moment' when my students figure it out, finishing a task, unexpected call or gift from old friends and remembering the old good days.
I smile when I see the children playing innocently. A probable reason for this is that the peaceful and the happy scene of the outside world makes me the same.
Smiling in a positive frame of mind is very infectious and spreads an 'aura of positive feelings' around you. It melts the anger in a person who approaches you with the same, it makes a communication proceed with ease and tends to develop a healthy relationship not only with your kith and kind but any person, in general. It injects a sense of Optimism even in persons who have lost hope and also results in having a healthy and friendly relationship. "A beautiful smile brings a silver lining even after the darkest nights".
The face usually reflects the state of mind. Why? It may be necessary to ask the creator. Nevertheless, some smile are artificial and do not reflect our inner state.
Smile is the outburst of our inner feelings. This is born out of excitement or anxiety. It can be positive or negative. I smile when I am happy or when I am surprised. Personalities differ greatly!
Smile five times each day at somebody you truly would prefer not to smile at; do it for peace. Many years back this peaceful and smiling lady declared this thing.
While lots of research on smiles triggering happiness was performed in the last half-century, that spurt of interest was actually a renewed interest in the topic. The theory goes back to Darwin, who proposed in the 19th century that facial expressions didn't only reflect emotions, but also caused them.
Smile reflect inside beautiful feeling of a person in most cases,whereas some times we smile to hide bitter feeling from a hard situation we met in our day.
May be genuine smile brings happiness. But nowadays, you can't interpret smiles again, most are just artificial. Some will be smiling with you and setting trap for you behind. From experience, people that smile and laugh without season are more dangerous than those that does intermittently. This is my own opinion and view. Best wishes.....