Idiom Magic:當然啦! And how!

【明報專訊】"You have been exceptionally (異常地) good children today," Angela's mother said with a smile. "May I reward you with some ice cream?" Angela and Teddy were filled with joy. "And how!" Angela exclaimed. "And how!" Teddy shouted. As you have surely guessed, "and how!" does not mean No. In fact, it means just the opposite. It is a strong and positive way of saying YES!