The boys cannot know where the swallows go; and if you told them--what is true--that the swallows find their way every autumn through France, through Spain, over the Straits of Gibraltar, into Morocco, and some, I believe, over the great desert of Zahara into Negroland: and if you told them--what is true also--that the young swallows actually find their way into Africa without having been along the road before; because the old swallows go south a week or two first, and leave the young ones to guess out the way for themselves: if you told them that, then they would have a right to say, "Do you expect us to believe that?
That is much more wonderful than that the swallows should sleep in the pond." But is it?
Yes; to them.

They know that bats and dormice and other things sleep all the winter; so why should not swallows sleep?
They see the swallows about the water, and often dipping almost into it.

They know that fishes live under water, and that many insects--like May-flies and caddis-flies and water-beetles--live sometimes in the water, sometimes in the open air; and they cannot know--you do not know--what it is which prevents a bird's living under water.

So their guess is really a very fair one; no more silly than that of the savages, who when they first saw the white men's ships, with their huge sails, fancied they were enormous sea-birds; and when they heard the cannons fire, said that the ships spoke in thunder and lightning.

Their guess was wrong, but not silly; for it was the best guess they could make.
But I do know of one old woman who was silly.