|[ dunce cap|
The dunce cap, when worn, fixes your intelligence and wisdom to 6, and autocurses. It blocks the mind flayer's brain eating attack, but not its amnesia attack. Removing the cap will restore your intelligence and wisdom to their original values.
Wearing a dunce cap also prevents any change to your intelligence or wisdom; the message is "Your cap constricts briefly, then relaxes again."
Shopping while wearing a dunce cap will cause the shopkeeper to add an additional 1/3 markup to the price of each item, and only give you 1/3 of the base price when selling items. This is not in addition to the penalty for being a low-level Tourist or having a visible shirt.
The dunce cap is not a good piece of armor, but if your Int or Wis happens to be lower than 6, the dunce cap will be an improvement! If your brain is in danger of being eaten by a mind flayer, donning a dunce cap may actually be a good idea. The cornuthaum is only useful for wizards or pets, so non-wizards can ignore unidentified conical hats to completely avoid the risk of donning a dunce cap.
Perhaps its best use is to polymorph it into other magical armor.