The Doctor has ever been one for adventure. And for finding his way into trouble besides, so really it's hardly much of a surprise when the ground falls out from under him and he goes head over heels into a pit. Which is certainly undignified, yes. But as far as mishaps go he's certainly had worse; by the time Horatio ends up peering over the edge he's already most of the way up to his feet.

"Ah, no. Or not any worse than a bit of a blow to my pride, anyway. Although getting back out might be a little difficult with everything this wet."

Not that he won't give it his best effort, of course. But it's certainly not going to be the easiest of tasks, either.