Put a Grin above your Chin

Happiness: The Science behind Your Smile
You'll go a mile
If you just smile
It gives you style
That lasts a while

Frown if you will
A look to kill
Is not a thrill
It's nothing — nil

So put a grin
Above your chin
It's not a sin
And you will win

They'll wonder what
You may have tho't
Or if you've got
Some other plot