Killing, under neon tanks

Swallow this air, it's laced with carbon monoxide,
I hope you take a deep breath so your lungs collapse from the inside.
Swallow down this poison and watch your stomach drown,
I'll do this hands down so you lie lifeless without a sound.
(Without a sound)

Take this secret to your grave,
Either way, you'll be lying in it soon,
With my dagger in your back,
Take this secret to your grave,
Either way you'll be lying in it soon
With her lipstick on your neck.

Swallow this water,
Let its contents be a mystery,
But you'll know in time when its character starts to melt your insides
Don't be ashamed darling,
You'll be the only one that knows.
Except for him 'cause he'll be joining you to decay from the inside
(From the inside)

His body drops to the floor.
Just as you walk through the door,
Little do you know that in the closet lies his corpse,
You take a drink of the water he's left out,

What's in your heart?