Three old women are discussing how their memory isn't what it used to be.
The first woman says, "Sometimes, I'm in the elevator, and I don't remember if I'm going up or down."
"The second woman says, "sometimes, I have a bottle of mayonnaise in my hand, and I don't remember if I'm taking it out of the fridge or putting it back."
"The third woman says, "Well, I don't have any of those problems, knock wood," knocking on the table. "Oh, hold on a second, someone's at the door."