Memory Game Idioms 2Online version Players will try to match the idiom with it's meaning. by Lunarn Smith It’s not rocket science Good idea or invention Once in a blue moon Hold your horses Burn the midnight oil Don’t start problems or cause trouble Cost an arm and a leg Tell a secret It’s not hard. Work until late at night Happens very rarely; uncommon Very expensive Let sleeping dogs lie Ants in one’s pants Wait and be patient Let the cat out of the bag Best thing since sliced bread Can’t stay calm (relax) because you’re nervous