You wouldn't believe some of the things people say to conversational interfaces.
A long time ago – I'm talking early 2000s – I designed a voice UI for a train timetable information system. It was a phone line, you called it up, told it where you were travelling to and from, and it gave you the information you needed.
After launch, I would listen to the odd call at random to see how it was handling things. I distinctly remember one case where, when asked their destination, the user said "I'm going to a funeral".
Now, when somebody said something outside the scope of the expected responses, we would reprompt them up to twice more with a bit of extra guidance. I'm proud to say that, even though this caller started way off course, the system steered them back and they ended up going away with the information they needed.
That's actually a danger of making your conversational interfaces too human-like - people then talk to them like they're humans, and it doesn't go well. You're better to make things a little stiff and robotic, so as to manage their expectations and make them understand that they need to constrain their answers a bit to get what they need. It might feel less natural, but everybody goes home happier at the end of the day.
