A Zipper Mouth refers to when a person has a Zipper Over where there mouth should be. This can be for several reasons.

1. For the purposes of a visual gag to indicate that a character won't talk.
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2. A character in the post is wearing some variation of a Gimp Mask that features a Mouth Zipper as an improvised gag or for sensory deprivation.
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3. If a character in question happens to be an animate inanimate or happens to be a part of a race that typically has zipper mouths, like the Pokemon Banette.
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4. Some combination of the above reasons.
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