"I told you," the Doctor said with a hint of impatience. "There are no such things as ghosts. They can't hurt you because they don't exist."
"That's such a comfort," Jack said, staring pointedly at an ominous blotch on the stonework in front of the fire. "Whatever tries to kill us won't be a ghost."
The Doctor beamed at him. "Right!" At Jack's frown he scoffed, "Ah, I've got everything we need right here." With a manic grin, he pulled out a bag of marshmallows and three antique toasting forks. "See?"