[ But blue is so aesthetically pleasing! And perfectly acceptable. But then, by any definition of the word, the Doctor can't necessarily or responsibly be called grown or mature. ]

I've seen mutations in other species across the universe, co-existing where one suddenly has an ability the other doesn't, branching off in a different direction forward. Evolution — brilliant. And there are others, you said, but all with different abilities?

Ah — to generate and manipulate metal like that, it must drain you? Does it hurt? Sorry! Loads of questions, that's me.

[ He's seen so much in the universe and naturally, all species evolve in vastly different ways, but he's not yet come across human or humanoid species evolved in quite this way before, so he's fascinated. And wondering what it must feel like; as natural as breathing, or absolutely draining to use that power? ]