"Oh! OH! You're a ghost! Well, that explains it," the Doctor grinned at himself for finally working it out before it fell a bit. "Sorry," he added almost as an afterthought.
"Yes... leaving the ones you love and care about, never easy," he said softly. "Nor is watching them die for that matter.." He shook his head to clear those particular thoughts from his mind.
"Anyway... So, what do you do to occupy yourself here then? Besides kicking stones at unsuspecting people," he asked with a wry smile.