The Doctor is nonplussed by anything at this point. Well, at least not that he'd willingly show strangers. Friends and companions? That's a different story entirely.

He realises that Marco doesn't get it. But that's fine, he's well past explaining things to others as well. But he'll answer the last question.

"One of my senses has been taken from me. This is the only way to give me some semblance of it."