River accepts the handkerchief solemnly. Her heart's not entirely in the joke, though.

It's been a long day. And now that she's sitting, now that she's stopped moving, she can be exhausted, and she can remember Milliways.

Milliways, dying, despite everything they tried to do. Too little, too late, and maybe nothing would have been enough; it doesn't matter now.

She doesn't say that. She nods, a little, and twists around to give Simon better access to her leg.