More and more, Amy liked this Donna woman. Her reaction to Amy's comments regarding River and the Doctor's flirting made Amy finally crack a laugh, because her description was so apt. It did often seem like River (and the Doctor too, for that matter) couldn't "stop speaking rubbish for ten seconds."
"I know," Amy answered Donna, still laughing, "they're perfect for each other."
As Tonks rejoined them, Amy took a moment to catch her breath before tying to explain what she'd meant about the Doctor changing. "Timelords have this thing they do when they're dyin', where their whole body changes. So then, instead of dying, they start over again as someone new." Amy had only seen it once before, and even then... well, she didn't want to think about that. "It's not like you where he could change whenever an' however he likes, but after he's regenerated-- tha's what it's called, regeneratin'-- there's a load of energy left over an' he can be kind of weird for a while until everything settles in." With a smile in Donna's direction, she finished with, "Not that he isn't always a bit weird."