This is what they see:

River leaps through the cargo bay on tip-toe. She takes tiny, mincing steps, balancing on the edge of a toe, than stretching out her leg, careful to never let heel touch ground. She leans forward, sways precariously, and regains balance. Then, in a bounding leap, she clears a small container with a flourish of her arms, triumphant, and squats to begin patting at air. Jayne, Book, and Mal are shifting crates around, ignoring her, and she doesn't notice them.

She pokes the ground. Prods it. Caresses it. Whispers, "Yes, yes. I am. You need to listen to your head more. Both of them. We are. We will be."

She smiles, light and loving. Overhead Kaylee watches her, and for some reason the engineer is smiling, too, but doesn't quite know why.

This is what River sees:

River is in a river. It is light, not rushing, a shallow, bubbling murmur of cool, clear liquid over gray rocks. Her feet should not be wet, because she is in the cargo bay, and if she leaves wet footprints Mal will be mad. The fact that a very wet stream is also in the cargo bay is entirely irrelevant.

So she's careful to step on the slick rocks that stick out of the water, some tiny and close, some large and far away. Finally she clears the greatest gap, sprouting white albatross wings to hover onto dry land.

She is greeted by tiny, solemn creatures, things of shifting light and radiance and sorrow. She cannot see them, but they are beautiful, and she knows in some intrinsic way that the creatures are people. She bends, patting them lovingly as the creatures looks up with liquid eyes.

They are tall and short, male and female, dark and light. Some are happy and some are grim, at least on the outside, but all bear scars. And they're all clasping hands. Some (most) hide this fact, but it's true, and she smiles.

One of the invisible figures looks at her solemnly. "We're home, aren't we?" He asks, and her brother's voice – the deeper voice he speaks with in his mind – comes out.

"Yes, yes."

"Ain't sure," says a bubbly-tired one.

"I am."

"Ah don' want any uh' you here," the most scarred light lies. The creature's head starts hitting itself. He is invisible. River frowns, but not in confusion.

"You need to listen to your head more," she chides, because the light is being very silly. "Both of them," she adds, because why doesn't he just talk to the pretty one already?

"'Is a crew, not a gorram family."

This, from the big dark one. River laughs, because he doesn't understand, not yet, but, "We are. We will be."

And she smiles, because she knows, like she knows everything special and terrible, that it's true.