I agree. My mother never gets my jokes, but the poor thing laughs like crazy at everything I say just in case one is a joke. I love her so much, she tries so hard to be hip. I could say "I'm going to go have surgery to remove a blockage in my heart" and she would laugh, just in case.....
I think it comes from many years of us making fun of her for not getting any jokes.
Poor mommy.