Analysis of Butterfly Laughter

In the middle of our porridge plates
There was a blue butterfly painted
And each morning we tried who should reach the
          butterfly first.
Then the Grandmother said:  "Do not eat the poor
          butterfly."
That made us laugh.
Always she said it and always it started us laughing.
It seemed such a sweet little joke.
I was certain that one fine morning
The butterfly would fly out of our plates,
Laughing the teeniest laugh in the world,
And perch on the Grandmother's lap.