I like to ask about their passions outside of work. Video games? Sports? Communities they may be a part of?

I am not looking for passions that align with the company, I am looking for passion itself. Does this person like to dig into the details and figure out how something works and how they can make it better or do they just like something and not show much deeper interest? Do they tinker or try to make things better on the things they are passionate about? Do they even have things they are passionate about? (You'd be surprised how many people can't really answer this question, even in casual conversation.)

It's not full proof, but I've found that people that go the extra mile, people that are passionate and inquisitive and not always happy with the status quo, are people that are more likely to take the initiative when working on a project for me. At that point, it's my job to spark their interest in the product so they will (hopefully) apply that passion in the same way.