That would be one of the first signs they would show of superior intelligence.

Look! I believe there are some of them.

Do you see those holes in the mountain-side there?
And there they are, something like gorillas, only twice as big, and up the trees, too--and what trees! They must be seven or eight hundred feet high." "Tree-men and cave-dwellers, and ancestors of the future royal race of Saturn, I suppose!" said Redgrave.

"They don't look very nice, do they?
Still, there's no doubt about their being far superior in intelligence to those other brutes we saw.

Evidently this atmosphere is too thin for the two-headed jelly-fishes and the saurians to breathe.