"Not Ready to Die" comes off of the Call of Duty: Black Ops "Escalation" map pack and hasn't been released as a radio single but is available on iTunes.

Revolver magazine asked vocalist M. Shadows when the track was written:

We had a little break between the Nightmare After Christmas tour and the Welcome to the Family tour. So it was written, like, in four days that we had off. So it was pretty rushed. It was pretty incredible, though, because we really wanted to do it. It was written, like, a month or two ago.

Here's what he had to say when asked what the song is about:

Oh, well, the song is about the game. There’s a full backstory to what [the makers of Call of Duty] been doing for years with their “Zombies” series. I’m a big fan of the game, I play it all the time, so I got caught up in the story. They sent me over the full storyline, so I made sure it was going along the lines of the zombie story. So that’s what it’s about.

The "Escalation" map pack was released on May 3rd and I'm quite positive Critter is all over it.