From Team Fortress Wiki
Aughh, my head!
— The Soldier on gruesome skull-revealing operations.
The Zipperface is a community-created headwear item for the Soldier. It is an unzipped zipper attached to the Soldier's face that reveals his skull.
This item can only be worn around Halloween or during a Full Moon; at other times of the year, it does not appear in gameplay, unless the server has Halloween mode enabled. However, it can be equipped at any time and can still be viewed on the loadout screen even when it is not visible during games.
The Zipperface was contributed to the Steam Workshop under the name "The Boned-Appeal".
October 26, 2012 Patch (Spectral Halloween Special)
- [Undocumented] The Zipperface was added to the game.
- This item was submitted with two different styles, the second called "Appalling", which would have zipped up the zipper.
- Pow-zoop! Zipperface! in the item's decription is a reference to some of the Bombinomicon's voice responses.