What Festers

I've seen them lurking on the horizon...
Skulking in the shadows...
Feeding on mere morsels...
And with all of the bull,
Imagine the madness 
They never get full... 
Like the bottomless pits
Of the loathsome undead... 
Urged to devour your heart or your head... 
Foul, graceless and grossly unread...
Black as the night in their blood if they bled...
Though I digress I confess that it's best to say less...
Of the fiends in your dreams or your nightmares made flesh...
For even the sweetest of dishes go sour...
When giving a glutton a semblance of power