Cow

Cows are a common in-joke in many of the Call of Duty games, especially in some of the earlier games in the series with levels that take place in Normandy. This prompted the developers to jokingly put "No cows were harmed in the making of this game" in the credits. They are featured extensively in games such as Call of Duty 2, Call of Duty 3, and Call of Duty: Modern Warfare 2. They appear in many multiplayer maps as well such as Rundown and Wasteland. The cows also make an appearance in Call of Duty 4: Modern Warfare in the level Safehouse in the fields near the barn.

An easter egg, known as the "Giant Cow" is, as the name suggests, a giant cow. It is an oversized cow with a large bell seen in Call of Duty: United Offensive. It is a secret in the level, and thus is not normally found.

The dead cows could be a reference to Saving Private Ryan, where at one point the team runs out into an open field with dead cows lying around.