Doctor... [When the Doctor tells her everything's fine and perfectly normal, Donna begins to worry. But now he's away from his scroll. Brilliant.

The mare purses her lips before rolling up the scroll and attempting to tap her foot impatiently. This doesn't really work as a pony, so she settles for pacing. When she hears the clatter of running hooves, she looks over to see the Doctor in his full ridiculously equine glory.]

Doctor, over here! Where are we, and why don't we look like ourselves? Is this that Chameleons circuit you mentioned?