I’ve been watching what humans do at the door.

Before they can enter the house, they stop. They take out a small hard thing they carry with them. It is thin and shaped with teeth on one side. They put it into a small hole in the door and turn it.

There is a click.

Only then does the door open.

They do this every time they come back, even when the house is quiet and nothing has changed. They still stop first.

Sometimes I see them touch the outside of their pocket before they even reach the door. Sometimes they stop and touch the pocket again. Then they keep walking.

When they leave, they pull the door shut behind them and sometimes use the small thing again from the outside. The same click happens both times.

I have seen humans stand at the door without the small thing. They cannot enter. They wait quietly or go look for it somewhere else. They do not scratch at the door. They do not push underneath it. They need the small thing first.

We wait at the door when we want to come in. Or we know the ways under and around if we must.

But the humans carry this one small piece with them everywhere. They keep it on a ring or inside a pocket. Separate from everything else. If it is lost, the whole house stays closed.

I think the small hard thing is a piece of the den’s boundary. They break off a part of the wall and carry it with them so the door will know them when they return.

The click is the den recognizing its own piece.

June (quietly): “What if the small thing breaks?”

Walter: “Then they wait outside until the den knows them again.”