Sure... but then it might make them uncomfortable if they can't think of one. I don't think there is a full-proof system for this, and it's not even a bad thing, maybe it's meant to be that some people have common interests in some aspects and different in others.
I guess I will have judged you incorrectly then - I never claimed my system was perfect!
Perhaps another thing to try would be to ask them to tell you a joke ?
(I'm a bad example though, I don't remember/collect/write them.. a mere consumer.)
Sure... but then it might make them uncomfortable if they can't think of one. I don't think there is a full-proof system for this, and it's not even a bad thing, maybe it's meant to be that some people have common interests in some aspects and different in others.