Mustache

Mustaches are items that appear on Zombies, Flag Zombies, Conehead Zombies, Buckethead Zombies, Screen Door Zombies and Ducky Tube Zombies. When you type "mustache" while the game is being played. You can activate this code at any time in the game. There are three types of mustaches, as seen below.

Achievements
If you do this, in Steam you will unlock the achievement Ask Me About Mustache Mode. In  the GOTY edition, this was simplified to Mustache Mode. These achievements are regarded as the easiest achievement in the game.

Trivia

 * If the Zombies approch a Garlic they will not make disgusted face when you turn on the Mustache Mode.