Awesome find on level 18: Mill on TNT! [zombie]

I was clipping around and I found a dark area behind 3 moving window things and I clipped through the left and middle windows, and in each one I found myself standing there. I shot myself and it hurt me and I killed myself and then I was dead but I could still walk around without a gun. Is this a glitch? Or has anyone else seen it?
I a couple minutes, I will attatch a saved game if I figure out how

This is the zombie effect, which has been known about for a long time and is well documented. It is a cool effect though, no question.

See Death on this page.

I've recorded a few zombie demos myself - see this thread for instance.