Note

On every ninth level of every area, and after defeating Dr. Zomboss, the zombies drop a note. Each note proceeds a tenth level, the last level of a stage, and alerts you to the fact that the next level will be a Conveyor-belt Level. The normal notes have horrible grammar and handwriting, but the note before the final boss has excellent grammar and wonderful cursive handwriting, with Brush Script style, because Dr. Zomboss, your main enemy in this level, is intelligent.

Help note
In addition to the normal notes, there is another note located on the main menu, under the help sign. If you click on the help sign it will show you a note, infamously known as the Help Note, obviously written by a zombie saying that to win the game you are supposed to let the zombies in your house, which would make you lose instead. In smaller print, it tells you that the help note is brought to you by the zombies.

Trivia

 * The note the player recieves before facing Dr. Zomboss has a background on a lawn, instead of the roof, where it was obtained.
 * The note you get in the Fog Levels says that it is your mother. This is the only place where it says the player has a mother in the game but the note was written by the zombies so it is unknown if its true or not if the players mom is still around.
 * The zombies ask you to leave your front door open and your lawn unguarded while you leave the house, but the zombies can't eat your brains if you're not in the house so it seems a bit pointless.