mylipsaresealed ''Mum's the word'' "I won't tell a soul" "I won't tell a soul!" Secret assurance "Your secret's safe with me" "Your secret is safe with me" "I'll never tell" "I'll never tell a soul" "Don't tell a soul" reply Reply to 20- or 37-Across "Shhhh!" response Pledge of confidentiality "Mum's the word, friend!" Disguised in Emerald Isle, a spy: Tees won't blab Non-speaking line? Mum's the word "Mum's the word" "Mum's the word!"