My Favorite Glitch is called ghost machine gun, It is on the map Foy in Call of Duty: United Offensive. It is at trp 10, it is that blown out building that is adjacent to the road in front of the church with the machine gun. The trick is to get right over the machine gun on the partly exposed roof. Go Prone and press F, it looks like no one is on the machine gun but ur firing though the sights. For me, It gets laggy when you look at the church. The Enemy can still see your body on top of the roof, and even if they don't see you, one or two hits with a tank or anti-tank weapon on teh machine gun will take you out. Doing this is possible in any Call of Duty game with a covering over the machine gun but it's still possible to man it. In Call of Duty 4, I know it in Ambush.