"The no-air doesn't break the balloon, the helium or air inside it would. Because it can push the balloon completely unchecked. And it's likely to push it to the point where the balloon breaks from the strain."

"Why does the helium in a balloon push just the right amount against the air so it doesn't squish in from the air pushing or break open from the helium pushing?" She gestures at the remaining intact balloons.

"Well, the person who filled it was in charge of just how much helium went into the balloon. And they chose an amount that would result in an inflated balloon, but not a broken one."

"Oh! That makes sense."

"I would be very disappointed in the world if it didn't make sense," agrees Lynn, sagely. "I'm of the opinion that the things that seem like they don't make sense are things that we don't know everything about. So of course they don't make sense, we're missing half of the required information to understand them."

"Like why I look like a human but I can hold my breath and my hair does the thing and stuff."

"Exactly. Humans can hold their breath, too, just not as long as you can. Though maybe you can hold yours indefinitely, I'm not sure."

"How long is that?"

"It varies, from person to person. Usually it's around one minute, longer if they practice. I think the record for holding one's breath above water is ten minutes or so."

"Is it different for under water?"

"A little. I'm not quite sure of the specifics, but I think there's something involved with a human's body adapting to swimming and purposely using less oxygen when underwater."

"I don't think I have been swimming," muses Astrid.

"Would you like to go swimming?"

"Maybe. But what if I am a kind of thing that can't swim?"

"Hmm. Then I would take you to a private place to try it, and if you are a thing that can't swim I would pull you out before anything bad happens. Or, if you like, we can not go swimming and not press the issue."

"Where do people swim?"

"Oceans, some lakes, pools made specifically for that purpose - I think some rivers, too, but I wouldn't take you there because often those have litter strewn about and I don't want to risk your safety."

"Is litter dangerous?"

"Not in a - ostentatious, obvious way. It does not go out and mug people for lunch money. But litter isn't in a place it's supposed to be. So, a broken glass bottle could be in a place you didn't expect, and it could cut you if you step on it without knowing it's there. Or, an animal could mistake the litter for something edible and eat it, and then die because they weren't meant to eat something like that."

"Why can't animals tell what is food for them?"

"Well, their methods of identification are off sometimes. They go by bright color or texture or smell, thinking it's like something they've had before, but it turns out that it's not."

"That's not how I tell what's food."

"... Huh. That's how I tell what's food," says Lynn. "That's interesting. Also useful, it sounds like your identification is more accurate."

"If it wasn't I might eat things that aren't food. You just see what color things are and stuff? What if something was painted?"

"I don't usually eat things because of their color," snickers Lynn. "If something apple shaped was painted to look like an apple, it might briefly fool me if it was done well, but I have a very good idea of what apples look like. So I can notice what is different about it from the apples that I know and realize that it's not food."