What is your most productive interview question?

I like to ask "what do some people assume about you that's wrong?"

It could allay any subconscious fears I have, or even open a Pandora's Box of insecurities and weaknesses you don't get from "tell me your biggest weakness".

(Low-key "would you like some water?" tells me if they think before they speak. If they say "no, thanks", then 15 minutes have a coughing fit, it loses points. Always accept a drink, even if you don't need it now... maybe it shows you prepare for unlikely but potential pitfalls.)