Subject-auxiliary inversion in echo tags

Echo tags are used in reaction to an affirmative or negative statement. They are formed in the same way as question tags (with the inversion of the subject and auxiliary), but an affirmative statement is followed by an affirmative tag and a negative statement is followed by a negative tag:

"I'm so hungry!" "Oh, are you?"
"I'm sorry, I can't stay any longer." "Can't you?"
"They always have lunch at 12." "Do they really?"
"My sister has just passed her driving test." "Has she?"

Rising intonation in the tag can express interest, while falling intonation can show indifference.