Látható&láthatatlan

Smiling is infectious,
You catch it like the flu,
When someone smiled at me today,
I started smiling too.
I passed around the corner,
and someone saw my grin,
When he smiled I realised,
I'd passed it on to him.
I thought about that smile,
Then I realised its worth,
A single smile just like mine,
Could travel round the earth.
So if you feel a smile begin,
Don't leave it undetected -
Let's start an epidemic quick
And get the world infected!