The Whisper-Stealer

The world has no shortage of dangers to be found should one venture where they don't belong, but that does not mean stories told by parents to scare their children into behaving properly don't still serve their purpose.   This is one such story, meant to frighten children away from telling lies and spreading rumors:  
There once was a boy who uttered a whisper,
A harmful secret told to his dear sister,
"Don't tell anyone!" he said with a hush,
"I would never!" she replied in a rush.   There once was a girl who muttered a secret
Even though she said she would keep it
"It's between friends?" she said with a hope,
"Of course it is!" said the friend as a joke.   There once was a friend who spoke of a rumor,
A once-secretive thing in which they found humor,
"Can you believe it?" they asked with some glee,
"If I heard it from you!" said a stranger or three.   And with each telling this small whisper grew,
And little remained that was honest or true.
As the story repeated it began to grow dark,
And unknown to the boy he developed a mark.   What was once was a whisper was now a known tale
And the boy's efforts to stop it continued to fail.
The whole town now knew the secret un-kept
And the young boy soon ran away and wept.   He found a small cave in which he could hide
Secluding himself from the stories outside.
He first told the secret on little more than a whim
And feared everyone would learn it was him.   Deep underground the boy became lost
As he sought to avoid paying the cost
Of the rumor he started in his small town,
A whisper he uttered that soon spread around.   With each day in the cave the mark grew in size
And the light of the sun soon left the boy's eyes.
He feasted on on bugs and skittering pests,
And crawled through the caves without need for rest.   And before long this boy forgot his own name,
And all of his memories but one filled with shame.
And in him grew a hunger most grim,
A taste for the flesh of children like him.   He seldom leaves the dark of his cave,
But his time in the shadows has made him more brave.
Sometimes he gets hungry, and follows the smell
Of misbehaved children and false stories they tell.   Nothing remains of the small boy from before,
Now a twisted thing that crawls under the floor.
So be truthful young one, for there is no healer
That can save you from the teeth of the Whisper-Stealer!