This is a glitch to get under the map in DEATH TOLL at the CHURCH.
It's really cool when you play on EXPERT because when the horde comes, they can't get to you, and you can just shoot them from under the map. it's the easy way to get through the church part.

At the end of the video you can see me under the graveyard part, and you can just shoot through the ground, it's kinda like call of duty world at war, you could go under the map and kill everybody without them being able to hit you back lol..

P.S Sorry for the bad quality =) (less info)