This is the Play Dead code, it has the side effect of not being able to be knifed due to the fact you are not alive in the game, you can hear every one and they can hear you.

It looks like your dead to everyone else but on your screen your running around, you can knife others while you have this on but the function only lasts a second because your not standing on the other players screen.

Yes you can call it an Anti Knife but that's not the true intention of the code, it's an unexpected perk to the bigger picture.....