The whole idea of trans-dimensional exploration via the expedient of sending probes on blind jumps. In the CSP/Maretian metaverse, distances between universes have apparently no relationship with how different the universes are from each other. So universes the distance of a hydrogen atom's width apart can be normal, normal, almost normal, normal, normal, normal, TROUBLE. And the more you do this, the more likely you are to encounter forces of evil you aren't prepared to resist, like magical tyrants, evil giant space robots, warring piloted giant space robots, or vast and malevolent powers beyond mortal comprehension. And, eventually, you'll attract their notice. Which happens... twice in the same chapter.
Dragonfly's possible ability (or psychosis) to sense the feelings/thoughts of the inanimate. One of these voices is, of course, that of Mars- an actively murderous, malevolent Mars. Imagine what it feels like to be standing on a planet that is overtly and consciously hostile.
“I don’t know if you care,” Dragonfly said, “but Mars is talking again.”
Cherry Berry sighed. “What’s it saying? ‘Die’ again?”
“No,” Dragonfly said. “Hear the clicking of rocks? That’s what laughter sounds like in Old Changeling.”
The planet was laughing at them.
Remember that the pony castaways (and to a much lesser extent the dragon and the changeling) grew up believing that a totally controlled ecosystem, where plants, animals, and even the weather were carefully managed and controlled on a day-to-day basis, was normal. Their very definition of terror is wild places like the Everfree Forest, which is renowned specifically because it's a place in the center of Equestria the ponies can't control. When it finally sinks in that Mark Watney's entire universe is, by pony standards, wild, their first reaction is to feel sorry for Mark for living in such a terrifying world. Their second reaction, after he casually makes it clear that he's an end product of that wild state, is a moment of instant trepidation.
The ponies froze mid-hug. "Mark," Starlight said carefully, "are you saying you’re one of the monsters of the Free Forever Forest?" "Well... I’m not saying I'm not..." The group hug broke up quite abruptly after that. Fireball shook his head. "Ponies," he muttered.
