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