They usually have to wear it with a straitjacket. Hannibal Lecter was fond of wearing them. Here's a picture of what they look like: http://upload.wikimedia.org/wikipedia/en/d/df/Hannibal_Rising_1.jpg
I am NOT talking about the kinds utilised in fetish bondage.
Very best answer:
Answer by Javier H
a muzzle, just like dogs wear
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Orignal From: What is the mask called that insane people sometimes have to wear so they don't bite people?