Why does Thay say that smiling is the most basic kind of peace work?  A smile not only helps to relax ourselves, releasing our own tension and anxiety so that we can touch more peace. The smile on our face will bring more pleasant feelings to others.

Thay sees smiling as integral to mindfulness practice:

A smile is a form of yoga practice – mouth yoga.  We all know that when we are happy, we smile.  However, our body instead of our spirit can also initiate the smile intentionally.  Even when we are feeling bad, if we try to smile, we will suffer less.  

When you have joy and smile, that is not a practice as it is natural.  But, if we don’t have joy and we still smile, that is real practice.

When people see us with muscle tensions on our face, they don’t see us like a flower.  People are afraid to connect with us.  We look more like a bomb than a flower. But if we know how to smile, in just one second, all these muscles are relaxed and your face looks like a flower again. It’s wonderful!

Look into the mirror and practice smiling.  You will feel that you are released from the grip of the anger, despair, stress or whatever negative emotions you have at that moment.  Smiling like this is peace work, bringing more peace to yourself and all those around you.