(Has the) cat got your tongue?
A humorous question directed at one who is not speaking very much or at all. A: "What's wrong, sonny? Cat got your tongue?" B: "Oh, he's just shy around new people, that's all."
(Has the) Cat got your tongue?
Why are you not saying anything? (Often said by adults to children.) Grandpa used to terrify me, both because he was big and fierce-looking and because he usually greeted me by bellowing, "Cat got your tongue?" Hi, Lisa! How are you? How's your husband? Are you surprised to see me? What's the matter, has the cat got your tongue?
(has the) cat got your tongue?
(informal) why don’t you say anything?: What’s the matter — cat got your tongue?