"All right, Peter," Mr. Caxton said. "Suppose we take a look at the planet Mars. It's the planet of your birth, remember. A boy with real intelligence should know a great deal about the planet of his birth, shouldn't he?"
Peter gulped and stared, knowing that Mr. Caxton did not really expect an answer.
"Peter," Mr. Caxton went on. "The first space rocket reached Mars in nineteen ninety-seven. This is the year twenty fifty-three. Fifty years is a long time, Peter. In all those years no man or boy has ever seen a Martian animal.
"Do you know why, Peter?" Mr. Caxton gave Peter's arm a slight wrench. "I'll tell you why. A man requires so much gaseous oxygen to support his life that he can't walk twenty yards on Mars without an oxygen mask. He'd drop dead if he tried to walk a mile. You can build fires if you bank them carefully, but a man needs more oxygen than a fire."
Mr. Caxton's eyes narrowed in malicious triumph. "No animal the size of man or larger could exist on Mars without some kind of natural oxygenating apparatus built into its body.
"A bird? Peter, I'm going to be completely honest with you. A certain kind of bird might just possibly be able to survive on Mars, but it would have to get along on very little oxygen."
With an effort Peter summoned the courage to interrupt Mr. Caxton with a quite unnecessary reminder. "It was a bird, Mr. Caxton. I told you it had feathers!"
"Yes indeed, Peter. It was a bird you saw. You say you saw a huge bird standing in the doorway. Do you realize what a perfect pit you have just dug for yourself? Do you know what a Martian bird would look like? Have you ever tried to imagine how a real scientist feels when he knows that he can't be wrong? Here, I'll show you!"
With his gaze fixed triumphantly on Tommy Mr. Caxton removed a small writing pad from his weather jacket, and proceeded to draw upon it. Mr. Caxton used an ordinary lead pencil, and that his skill as an artist was of no mean order could be seen almost instantly.
With a few deft strokes Mr. Caxton traced out on the smooth paper a shape of incredible lightness and grace, a shape so fragile, slender and spiraling that only a miracle of the glass-blower's art could have translated it into three-dimensional reality.