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 consistency, answers should be in all lower cased letters.

Category: PHRASES OF DEATH 
Clue: Completing 2 tasks with one action is "killing 2" of these "with one stone"
birds

Category: SUCH GOOD CHEMISTRY 
Clue: A U.S. nuclear weapon using this element, Co, has been termed a doomsday device, as it would wipe out life on Earth
cobalt

Category: MYTH ME? 
Clue: Hera punished this gossipy handmaiden by taking away her power to originate speech

echo