An old tired dog...

An old, tired-looking dog wandered into the yard. I could tell from
his collar and well-fed belly that he had a home.
He followed me into the house, down the hall, and fell asleep in a corner.
An hour later, he went to the door, and I let him out.
The next day he was back, resumed his position in the hall, and slept
for an hour. This continued for several weeks.
Curious, I pinned a note to his collar: "Every afternoon your dog
comes to my house for a nap."
The next day he arrived with a different note pinned to his collar:
"He lives in a home with ten children -- he's trying to catch up on his sleep. Can I come with him tomorrow?"