Staying calm with patients who have unusual stories

So I was reading some Seneca the other day, all about managing emotions and staying composed. It got me thinking about how we apply that in real life. In my line of work as a dental lab tech, I deal with patients indirectly, but I hear all sorts of stories from the dentists I work with. The other day, one told me about a patient who was absolutely convinced aliens had performed their appendectomy. It’s one thing to read ancient philosophy, but how do you actually keep a straight face and stay professional in a moment like that? Has anyone else had a patient share a truly out-there belief during an appointment? How did you handle it without dismissing them or losing your cool? I’m genuinely curious about your approaches.