“I don’t know,” she said.  “Only every now and then I find myself thinking the most obvious thoughts.”

“We all do,” I answered, as I stroked my limpet gently.  The noise of our conversation had roused it, but a gentle stroking motion (I am told by those to whom it has confided) will frequently cause its muscles to relax.  “The great thing is not to speak them.  Still, you’d better tell me now.  What is it?”

“Well,” she said, her cheeks perhaps a little pinker than usual, “I was just thinking that life was very wonderful.  But it’s a silly thing to say.”

“It’s holiday time,” I reminded her.  “The need for sprinkling our remarks with thoughtful words like ‘economic’ and ‘sporadic’ is over for a bit.  Let us be silly.”  I scratched in the rock the goal to which I was urging my limpet and took out my watch.  “Three thirty-five.  I shall get him there by four.”

Celia was gazing at two baby fishes who played in and out a bunch of sea-weed.  Above the seaweed an anemone sat fatly.

“I suppose they’re all just as much alive as we are,” she said thoughtfully.  “They marry”—­I looked at my limpet with a new interest—­“and bring up families and go about their business, and it all means just as much to them as it does to us.”

“My limpet’s business affairs mean nothing to me,” I said firmly.  “I am only wrapped up in him as a sprinter.”

“Aren’t you going to try to move him again?”

“He’s not quite ready yet.  He still has his suspicions.”

Celia dropped into silence.  Her next question showed that she had left the pool for a moment.

“Are there any people in Mars?” she asked.

“People down here say that there aren’t.  A man told me the other day that he knew this for a fact.  On the other hand, people in Mars know for a fact that there isn’t anybody on the Earth.  Probably they are both wrong.”

“I should like to know a lot about things,” sighed Celia.  “Do you know anything about limpets?”

“Only that they stick like billy-o.”

“I suppose more about them is known than that?”

“I suppose so.  By people who have made a specialty of them.  For one who has preferred to amass general knowledge rather than to specialize, it is considered enough to know that they stick like billy-o.”

“You haven’t specialized in anything, have you?”

“Only in wives.”

Celia smiled and went on.  “How do you make a specialty of limpets?”

“Well, I suppose you—­er—­study them.  You sit down and—­and watch them.  Probably after dark they get up and do something.  And of course, in any case, you can always dissect one and see what he’s had for breakfast.  One way and another you get to know things about them.”

“They must have a lot of time for thinking,” said Celia, regarding my limpet with her head on one side.  “Tell me, how do they know that there are no men in Mars?”