Just pop them into regex101 or a similar tool, add sample data, see the mistake, fix the mistake, continue to do other stuff.
So you can ask them what they are passionate about outside of work. Something like:I'm really into reading sci-fi books. Is there anything you are passionate about outside your work?
Just pop them into regex101 or a similar tool, add sample data, see the mistake, fix the mistake, continue to do other stuff.