"Why. Are they really dangerous?"
"They're unpredictable," Syme told him. "They're built differently, and they think differently. They breathe like us, down in their caverns where there's air, but they also eat sand, and get their oxygen that way."
"Yes, I've heard about that," Tate said. "Iron oxide—very interesting metabolism." He got his energy pistol out of the compartment and strapped it on absently.
Syme turned the little sand car up a gentle rise towards the tortuous hill country in the distance. "Not only that," he continued. "They eat the damndest stuff. Lichens and fungi and tumble-grass off the deserts—all full of deadly poisons, from arsenic up the line to xopite. They seem intelligent enough—in their own way—but they never come near our cities and they either can't or won't learn Terrestrial. When the first colonists came here, they had to learn their crazy language. Every word of it can mean any one of a dozen different things, depending on the inflection you give it. I can speak it some, but not much. Nobody can. We don't think the same."
"So you think they might attack us?" Tate asked again, nervously.
"They might do anything," Syme said curtly. "Don't worry about it."
The hills were much closer than they had seemed, because of Mars' deceptively low horizon. In half an hour they were in the midst of a wilderness of fantastically eroded dunes and channels, laboring on sliding treads up the sides of steep hills only to slither down again on the other side.
Syme stopped the car abruptly as a deep, winding channel appeared across their path. "Gully," he announced. "Shall we cross it, or follow it?"
Tate peered through the steelite nose of the car. "Follow, I guess," he offered. "It seems to go more or less where we're going, and if we cross it we'll only come to a couple dozen more."