The golden years

I was having a nice conversation with my grandmother this afternoon in the dayroom at her nursing home, when she abruptly turned to her roommate. The following ensued:

G'ma: Do you know what we forgot to do?
Roomie: No, what?
G'ma: We forgot to check that thing off.
Roomie: Well you know, we sure did.

And they sat and nodded at each other in agreement. I don't know what "that thing" is, and I'm willing to bet they don't either.