I feel the need to disagree with you here, it's absolutely possible a candidate just doesn't have any questions, maybe they've done their research up front, or all their questions were asked during the interview, I wouldn't necessary correlate that with curiosity.
I've been in interviews where I had some questions up front, but they all got answered during the interview itself, either through natural conversation, or because the person interviewing touched on those topics.
> The question will be the same, the answer will be different.
Personally, especially when I know I'm having different interviews with different people, I ask the same question twice, just to evaluate their answers. If the answer to a question (e.g. Do engineers have a lot of input regarding technical decisions) is different between one of the engineers and the dev lead / CTO, then you know there's something wrong.
Especially at bigger companies, where I know the final interview will be with HR, it's interesting to ask questions regarding company policies or culture. You usually get very different answers.