A Smile

Smile

Definition: Form one's features into a pleased, kind, or amused expression, typically with the corners of the mouth turned up and the front teeth exposed.
A smile has the mystical power of turning someones day from bad to good in a split second

A warm smile is the universal language of kindness.-William Arthur Ward 
This is true in all forms of life, a smile is better than a nasty frown and can change someones world and trust you in all the ways possibles.
Once a day everyone has a bad day or a bad experience, and the only way available to respond to it is with a beautiful smile.