Three old ladies sit in a cafe - discussing their health.

First lady:  "You know, I'm getting really forgetful. This morning, I was standing at the top of the stairs, and I couldn't remember whether I had just come up or was about to go down."

Second lady:  "You think that's bad? The other day, I was sitting on the edge of my bed, and I couldn't remember whether I was going to sleep or had just woken up!"

Third lady, looking smug:  "Well, my memory is just as good as it's always been, knock on wood," she says, as she raps on the table. Then with a startled look on her face, she yells: "Who's there?"