My late dog, Ruth, lived to 16. In her last year, she developed Doggie Dementia along with a very slow gait, sort of like Tim Conway doing the Little Old Man.
She would pace into a room, stop, and stare blankly. We developed a whole routine:
"What's the matter? Lost your keys?"
"Ruth? Where are the invisible gophers?"
"Forgot what you came into the room for, did you?"