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.

Category: "O" YOU ANIMAL! 
Clue: It "coughs" out sediment by clapping its shell shut
oyster

Category: OLD HISTORY 
Clue: In this work Virgil wrote that "a woman is always a fickle, unstable thing"
the aeneid

Category: WHAT A COUNTRY! 
Clue: 1 of the 2 South American countries directly east of Ecuador

colombia or peru