As it was, the Doctor was still far from learning how to judge Illyria's moods. They tended to either swing in one direction or the other, it was very confusing. And yet still, it was a bit of a challenge, and after so many years on his own? A challenge was a nice change of pace.
More of a challenge than re-programming the TARDIS radiation detectors to search internal devices. That? Merely tedious.
He slid his reading glasses to the top of his head and ran his hands over his eyes. What time was it? TARDIS-time....bedtime? How long had he been working on his tinkering? And where had his mysteriously unpredictable commpanion wandered off to?