Why do you not speak?; Speak up and answer my question! (Folksy.)
Answer me! What's the matter, cat got your tongue?Why don't you speak up? Cat got your tongue?
cat got your tongue?
'why aren't you talking?'; used for mocking or asking why a temporary speechlessness has struck. Elliptical for 'has the cat got your tongue?'; generally addressed to a child but equally patronising when asked of an adult UK, 1911