You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

[EX Q]: Category: DESIGN 
Clue: Derived from scutum, the Latin for "shield", it's a shield bearing a coat of arms, or a metal plate around a keyhole
[EX A]: escutcheon

[EX Q]: Category: "O" YOU ANIMAL! 
Clue: It "coughs" out sediment by clapping its shell shut
[EX A]: oyster

[EX Q]: Category: DOUBLE-LETTER WORDS 
Clue: It's a combination of 2 metals; brass is one, combining copper & zinc
[EX A]:
alloy