and, putting his hands in his pockets, began to whistle.

"I think you might tell me _what_ kind of an animal a bird is, and why
it has feathers and can fly, instead of laughing," said Dodo in a shaky
voice; for her feelings were very tender and she remembered too late
what minerals are.

"Yes, tell her, Nat," said Olive, who came through the hall just then.
"Are you holding your knowledge tight in your pockets, or whistling to
keep from telling it?"

Nat scowled a minute and then said frankly, for every one was frank with
Olive, "I really don't know what sort of an animal a bird is, though I'm
sure it _is_ an animal. Don't you think Uncle Roy will tell us?"

"I'm sure he will be glad to, if he is not very busy, and he is seldom
too busy to talk of birds. He is writing a book now of all the things he
knows about them. Knock on the door, Dodo."

"I'm afraid to," said Dodo, clasping her hands behind her. "Mammy says
that room is _full_ of birds, and that we must never go in there.
Suppose when the door opens they should get out and fly away?"

"Mammy was right in telling you not to go in without asking, because
there are a great many books and papers there that father values, and
you might upset them. But the birds that are there are not alive. They
are dead birds that father has collected from all parts of
America--stuffed birds, such as you have seen in the glass cases in the
Museum."