second day.

"I was fair worn out, but Tweel seemed as fresh as ever, for all I never
saw him drink or eat. I think he could have crossed the Mare Chronium in
a couple of hours with those block-long nose dives of his, but he stuck
along with me. I offered him some water once or twice; he took the cup
from me and sucked the liquid into his beak, and then carefully squirted
it all back into the cup and gravely returned it.

"Just as we sighted Xanthus, or the cliffs that bounded it, one of those
nasty sand clouds blew along, not as bad as the one we had here, but
mean to travel against. I pulled the transparent flap of my thermo-skin
bag across my face and managed pretty well, and I noticed that Tweel
used some feathery appendages growing like a mustache at the base of his
beak to cover his nostrils, and some similar fuzz to shield his eyes."

"He is a desert creature!" ejaculated the little biologist, Leroy.

"Huh? Why?"

"He drink no water--he is adapt' for sand storm--"

"Proves nothing! There's not enough water to waste any where on this
desiccated pill called Mars. We'd call all of it desert on earth, you
know." He paused. "Anyway, after the sand storm blew over, a little wind
kept blowing in our faces, not strong enough to stir the sand. But
suddenly things came drifting along from the Xanthus cliffs--small,
transparent spheres, for all the world like glass tennis balls! But
light--they were almost light enough to float even in this thin
air--empty, too; at least, I cracked open a couple and nothing came out
but a bad smell. I asked Tweel about them, but all he said was 'No, no,
no,' which I took to mean that he knew nothing about them. So they went
bouncing by like tumbleweeds, or like soap bubbles, and we plugged on
toward Xanthus. Tweel pointed at one of the crystal balls once and said
'rock,' but I was too tired to argue with him. Later I discovered what
he meant.

"We came to the bottom of the Xanthus cliffs finally, when there wasn't
much daylight left. I decided to sleep on the plateau if possible;
anything dangerous, I reasoned, would be more likely to prowl through
the vegetation of the Mare Chronium than the sand of Xanthus. Not that
I'd seen a single sign of menace, except the rope-armed black thing that
had trapped Tweel, and apparently that didn't prowl at all, but lured
its victims within reach. It couldn't lure me while I slept, especially
as Tweel didn't seem to sleep at all, but simply sat