A SAD DOG THAT DOESN'T BARK

Our sad dog just doesn't bark,
Not even a whimper to hark.
Though never noisy like a lark,
He's so quiet, well off the mark.

An absence of a voice so stark,
Like a throat bitten by a shark.
Or is he hoarse from overbark?
Why so, I'm totally in the dark.

If life's been a walk in the park,
And contentment at benchmark,
Why the lacking in lively spark,
Having only silence for bulwark?