Possible Clues:

• Like cannibalism, e.g.
• Forbidden nocturnal animal goes round and round and round
• Not allowed cheers? I don't like that!
• Not permitted to raise bat, one short of a century?
• (Irrational) prohibition
• To be avoided
• Board game with forbidden words
• Ban volunteers and make noise of disapproval
• Verboten thing
• Subject to prohibition