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