Three older ladies were discussing the travails of getting older. One said, "Sometimes I catch myself with a jar of mayonnaise in my hand in front of the refrigerator and can't remember whether I need to put it away, or start making a sandwich."
The second lady chimed in, "Yes, sometimes I find myself on the landing of the stairs and can't remember whether I was on my way up or on my way down.
The third one responded, "Well, I'm glad I don't have that problem; knock on wood!" as she rapped her knuckles on the table, then told them "That must be the door, I'll get it!"
