How on earth do you keep a straight face?
I was once asked why some cows pee from the back and some from the middle... (Nothing to do with poultry, of course.) Deep breath - and explain.
Actually, I'd rather these people ask questions than not be interested at all. A lecturer in Australia once told me that it took one of his students (agriculture) a full year at uni to realise that cows have to have a calf before they start producing milk. What does that say about our society and what we learn at school, if not at home?