This appears to be a reference to the famous Portal game series line ' The cake is a lie'.

One of the tooltips on Diablo III loading screen states: 'Cow level is a lie'.

Nowadays, Blizzard still jokingly state that 'there is no Cow Level'. Before this level was in fact created for Diablo II, the Jersey's Jersey quest for Diablo: Hellfire was created to reference the rumor.

There were many rumors that there was a 'Secret Cow Level' in the original Diablo.

This section contains facts and trivia relevant to this article. The experience and item gains possible in the level were nerfed in Patch 1.10, and the level returned to its intended purpose as balanced and not a place to endlessly exploit for massive experience gain, thus avoiding any grinding. The cow level was the most popular place to level up in Patch 1.09, due to the huge numbers of cows, and the fact that their slow speed, low resistances, and clumping behavior made them very easy to kill in bunches. Furthermore, if someone already has killed the Cow King on the current difficulty in a previous game and decides to kill the King in another game, everyone within the Cow Level will be ineligible to get 'the kill.' If someone kills the Cow King for the first time on the current difficulty, all players within the Cow Level, partied or not, will get 'the kill' (he/she will be unable to create another portal to the Secret Cow Level on the same difficulty).

A rather special cow, named ' The Cow King', always appears in the level. The Secret Cow Level is a small area, full of Hell Bovines: bipedal cattle with polearms. For example, one must first beat the game (through Act IV in the original game or Act V in the expansion) on Normal difficulty before you can create the Secret Cow Level in a game of Normal difficulty. Players can only create this portal when playing at a difficulty level they have already completed. A red portal will appear in the Act I starting area. To create a portal to the secret level, combine Wirt's Leg and a Tome of Town Portal in the Horadric Cube. The Secret Cow Level, also known as the Moo Moo Farm, can be found in Diablo II (with or without the expansion Diablo II: Lord of Destruction).

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