You are not there to uncover all of their secrets or to make them squirm or to challenge them with unimportant questions. You are just trying to figure out if they are capable of doing the job and if they will be a cultural fit with your team.

So my serious question would be: how would you handle being given a very vague task with minimal direction? What would you do to get it done?

This would tell you if they are good at asking for help and if they can be a problem solver that can be independent and search for information.

Non-serious question: what's the best kind of easter candy? If they don't say Reese's peanut butter eggs then they can't be trusted.