To you such an idea may seem very strange. But if you were chased by
an enemy you might be glad to be able to swim under water, down to the
bottom of a pond, and slip inside a door which led to a winding hall,
which in its turn led upwards into your house.

Of course, your enemy might be able to swim as well as you. But maybe
he would think twice--or even three times--before he went prowling
through your crooked hall. For if you had enormous, strong, sharp
teeth--with which you could gnaw right through a tree--he would not
care to have you seize him as he poked his head around a corner in a
dark passage of a strange house.

It was in a house of that kind that Brownie Beaver lived. And he built
it himself, because he said he would rather have a neat, new house
than one of the big, old dwellings that had been built many years
before, when his great-great-grandfather had helped throw the dam
across the stream.

The dam was there still. It was so old that trees were growing on it.
And there was an odd thing about it: it was never finished. Though
Brownie Beaver was a young chap, he worked on the dam sometimes, like
all his neighbors. You see, the villagers kept making the dam wider.
And since it was built of sticks and mud, the water sometimes washed
bits of it away: so it had to be kept in repair.

If Brownie Beaver and his friends had neglected their dam, they would
have waked up some day and found that their pond was empty; and
without any water to hide their doorways they would have been safe no
longer.