[Lyric] Death Rattle (Angel's Milk)

I always thought a death rattle meant, like
A rattle from a snake
Before the snake bites you and kills you
But it turned out to mean
A rattle from yourself
After the snake has bitten your soul
And you've sunk so far down you can't feel anything
And the rattle spreads through your body
Like hell has been let lose within your bones
I'm still not actually sure what it means
I've heard it in about two songs
And I dont feel like looking it up right now on wikipedia