Bondye di, "tout pitit mwen yo, kouche!". Sèpan di, "Mwen deja atè."

This expression has always sounded clever and hilarious to me.  But I can't say that I know its exact meaning.
Bondye di, "tout pitit mwen yo, kouche!".  Sèpan di, "Mwen deja atè."
God says, "all my children, lie down!".  The serpent says, "I'm already on the ground."

Is the serpent mocking God?
Does "to lie down" mean "to taste misery on the ground" ?
I'm not sure about this one :)

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