Dickie Deer Mouse in "Making Ready For Winter"

But on the whole it was easy to discover whether a nest was deserted.
One look into it usually told the story. Eggs in a bird's nest meant that somebody79 must live there. And of course if Dickie saw a bird sitting on a nest he knew right away that he couldn't live there without having a fight first.
But a hole is different. One can't see what's at the bottom of it without going inside it.
And that is not always a pleasant thing to do.